I just had the CAT checked and you can see light go right through it, so that'* not an issue.

Interestingly, she started acting up once the engine was hot, and now she bogs down under load like before. So, it'* heat realted and something is messing with the fuel/air mixture because of that heat.

Ideas? Thanks in advance once again!

I don't think it'* a cat. More likely a MAF that'* dirty and/or bad.

I struggled with mine on my 1997 LeSabre. It would run fine cold, but once it got warmed up acceleration was just a suggestion until it got to about 3,000RPM .

Like setting a thermostat: I'd like 60MPH eventually, start now.

Anyways I finally replaced the MAF and it was night-and-day better. I had cleaned the MAF a few times but that never helped. The problem wasn't because of the temperature. It was because once it got warmed up, the PCM says "okay everything'* good and I've reached the desired temperature so I'm going to go with my most economical fuel mapping based on inputs from all of my sensors (including the MAF)" . The MAF was reading wrong so I ended up with poor readings being poor performance. Sounds similar to your issue.

I disconnected the MAF sensor -as I saw on-line that it is a way to test it out- and there was no difference in performance at all. Is this a valid way to test it?

I took it to a highly recommended transmission guy who said over the phone he'd give me a diagnosis for free. He stated that there is a spring and a valve that has been known to get gummed up and cause the very issue I described. I'm kinda at a loss now, so we'll see what he says and what else guys like you can do to assist.

I really appreciate all the feedback... this is a real hard -and frustrating- problem of which to find the actual cause.

If it runs better it could be the maf is bad but not necessarily. Tap on it, if the engine stumbles it'* bad.
That would be the shift valve(*) in the valve body. You can use a can of BG or Lucas trans fix and see if it helps.

It can be, but I usually refer to this test for poor running like stalling and running rough and MAF codes and that sort of thing. For my issue (above), that test told me nothing . . . and I didn't have any codes stored.

Tapping the MAF didn't do anything to the idle, as she actually idles fine... it'* under load that is the issue, but (look below):

So this.

Turns out, testing the MAF is not easy. I checked for power and signal (which was good on power and ground and seemed to have signal), cleaned it (thought it wasn't very dirty) and ran her with it disconnected and none of that told me anything that would lead one to believe it was an issue. The Check Engine light hadn't been on since I replaced the fuel pump either (disconnected the battery which probably caused the light to cease perhaps?). But she kept having real issues under load, really bad issues.

But I replaced the MAF with an AC Delco all plastic replacement, and she drives under load as designed now.

Go figure.... it was the final piece of the puzzle, that had absolutely no indicators and failed to show itself in testing.

You guys were correct.

I also put a bottle of Lucas Trans Oil in it as she'* at 93K and it seemed like a good idea anyway.

Thanks so much for your assistance!

Now I can get my truck back from my daughter, haha!

Glad you got it fixed!

. . . and yeah your truck will be much better to drive than a Lumina

It does, it sure does....

My daughter came by last night to get her car and return my truck, and she called me when she got home and stated it wouldn't go above 30.

I'm getting it again this AM to check it out again.

I. Just. Don't. Get. It. Quite frustrating.

Thanks in advance again!

I can check the fuel rail pressures, but it might be the injectors, whatever tells the injectors the amount of fuel to inject? ECM maybe?

First thing I'm going to do when I get it this AM is to check all the chassis/engine grounds as well as the connectors to the computer module.

I found a used one out of a '97 Lumina 3.1 for $35 here locally, I think I'll give that gamble a try.