Oh, sorry, I forgot to mention the el-cheap gauge (harbor freight) was leaking fuel inside the gauge, which MAY account for the drop in pressure.

UIM/LIM gaskets don't typically cause this code. However a vacuum leak is a vacuum leak and that can cause it. I've seen a bad TB gasket cause it. There'* very little to do wrong when putting on a TB gasket. Yet somehow my friend did manage to fold it over.

GM fuel pumps have a check valve built into them. The FSM states that you should key click on/off a number of times w/o starting the car to bleed air out fo the tester and then get the max reading. Walk away and come back 10 min later. I think a 5psi drop is all that'* expected. Yet I've never found a car that dropped to zero sitting to have any issues. Another thing I've noted with the FP testing is that key clicking isn't always accurate. That only shows the pumps ability to build pressure. When running it must also supply volume. I've had cars that passed the key click test and yet could manage their way down to 10psi driving. That could cause it.

Checking back in. The car has been on the road almost a week now, there are still no codes. UPS will be delivering the GenUine AC/Delco fuel pump assembly later today, I'll hopefully have time to install this weekend, and am hoping to post happy news about the stumble/cutout and occasional miss the car is still experiencing.

The unlikely Crank Position Sensor will get replaced too if I find the time, but one at a time so I'll know for sure which one cures the problem. (nervous laugh)

Thanks again for all the help and advise, I'm more of a euro-centric guy when it comes to machinery, but will offer any help I can to others on this board to reciprocate for the attention you guys have shown to my dilemma.

Good luck, keep us updated.

New fuel pump...didn't do much of anything, except make things more complicated than they should be, the "new" style pump comes with a different connector, so you have to splice in the new connector to the fuel pump harness. At least GM gives you the harness and connectors.

New style plug means you have to remove the solid post on the retainer ring, the post (made to bang on to get the ring on/off for pump service) lines up perfectly with the plug, which in the original configuration is higher. Chiseled it off with a brass chisel.

If it wasn't for these design "improvements", the pump replacement would have been a 10 minute job. Can't complain about the actual replacement on the Impala, fold down the rear seat..and THERE IT IS! Easiest fuel pump replacement I've ever encountered.

The fuel gauge now works for the first time in many years, that'* about the only difference.

Car still stalls out when cold, and has the occasional skip. Feels almost like it'* cutting out once in a while. I'm out of ideas, put some fuel injector cleaner in, and will run the 3M pressurized cleaner through when I get a chance, but I don't think it'll make any difference.

I'm officially stumped. No codes, no pending codes. I think I'm going to have to bite the bullet and get one of those scanner programs and hook it up to a portable computer in real time and see if I can catch anything when the miss/skip presents itself.

As I said before, this V6, as all V6'* usually do, was rock steady at idle and never a problem of this nature, now the idle has just a bit of trepadation and the rest.

I'm also thinking of re-replacing the new Fuel Pressure Regulator Coil/Ignition module, these took care of the no start problem, but may be causing these new problems. I got the crank position sensor, but it'* such a long shot I'm not going to bother to install, it'* not plug/play, have to make the engine module learn though a whole riga-marole I'm not up for anymore.

Man, I'm starting to really hate this POS.

Wow, long read, and disappointing. I hate gremlins that cause trouble.

I'm just tossing things out as I think of them...

O2 sensor? Check/replace?
Check for air leaks at fuel injector boss'*?
And last, but not least(doubtful, but someone else will say not to if need be) swap fuel injectors to back side and vice versa. (idea here is to see if the code will switch from one bank to the other)

Crank sensor can cause hiccups and stalls though. My car never actually died on me at lights etc, but it would commonly feel like a hiccup on the highway. About 2-3 times a day. Finally it gave me one crank code and I pulled the trigger. Never another issue. SignofZeta was in a similar situation.

Code never came back, the "lean bank 01" disappeared with the MAF swap out and there are still no codes.

I will do the crank sensor, I didn't realize there was some BTDT on this, I already bought it, just hope I won't need the tech2 to program it. This has now officially become a challenge!

I'm going to pull the air cleaner while I'm at it and check/clean the ECU contacts, using birdshot in this shotgun now.

Thanks for the help, I'll keep you posted.

You shouldn't need a tech2. Most car forum guys will tell you that you need to case learn the car after you do this..but that'* only to super optimize the pcm'* knowledge of where the crank position is.. Typically there is no issue and I don't bother to case learn my own vehicles unless there'* something very off.

Update.

New temperature sender and connector...did nothing. Car still ran rough at idle and had cutout and bucking until it got up to temperature. I did a couple other things too, but since they yielded no results either I'll keep it short.

It seems that it MAY be a defective Ignition Control Module. When the car had the no-spark condition, I replaced the original Ignition Control Module with an aftermarket one. The car started, and I've been chasing the litany of problems ever since.

On a hunch, a complete hunch, I replaced the new Ignition Module with the old one, and it seems that the car is running fine when the engine is cold. The verdict is still out, as today was in the 70'* temp wise which might account for it, but I doubt it.

Thanks again for all the help, I'll check back in if the problem comes back, but I suspect it'* resolved. Gotta look at the upside though, just about everything that COULD fail at this age and mileage has been replaced and checked, so it should be good for another 100k and 10 years.