I have a '97 Chevy Suburban and I have had to replace the fuel pressure regulator every year for the last 6 years. I have noticed that the rpm'* fluctuate about 500 rpms while driving on the highway and it doesn't matter if you're on flat ground or going down hill. When I'm traveling a long distance (after about 75 miles) the check engine light will come on. I have had the fault codes tested and they are showing P0174, P0134 and P171.

Any suggestions why the fuel pressure regulator continually goes fails?

I'm curious as to what'* leading you to changing out the FPR.

2 of those codes are for a lean condition on both banks or you have too much O2 in your exhaust. Which is weird because your 3rd code is for a inactive B1 S1 O2 sensor.

A coworker from the fleet maintenance department said that the FPR was causing a problem a few years back and it seemed like it was doing the same thing again. However, I've discovered that it is actually my overdrive going out in my transmission that is causing the fluctuation in the rpm'*.

But that doesn't resolve the issue with the check engine light and the codes. I have noted that it seems to be using more oil and it'* not leaking or dripping it on the ground. I found oil pooled in my intake breather tube, cleaned it out and changed the pcv valve, but that doesn't seem to have resolved any issues. I remember a friend commenting about having issues with an older model 350 some years ago and he had to remove the intake and take off a sheet metal pan that is riveted to it and clean out a bunch of carbon deposits that were caked up. Could this be causing some of my issues? This is the original engine in this '97 suburban with 390,000 miles on it and I know that we have not removed he intake in the 12 years we have owned it.

Then your injector poppets are leaking badly. You more than likely need a new injector spider assembly. If you plan on keeping this for awhile, upgrade to the newer style injectors.