NJ_Tahoe

Hey Folks,
I have a 1996 Tahoe that is getting a P0308 code. In the past there was a right side too rich code that would come and go but could never determine what the cause was. Well last year started having problem with rough running/no power one day and receiving the P0308 code. Found a problem with valve in #8 cylinder.
Had cylinder head rebuilt, 8 plugs, dist cap/rotor/pickup, fuel regulator/filter, temp sensor, crank sensor, oxy sensor (not sure which one), and heater valve. Seemed to run ok but then started getting the P0308 code and rough running. Mechanic said troubleshooting pointed to injector problem. Had new complete updated spider injector assembly installed which seemed to fix the issue.
Truck seemd to run fine just going nearby around town. Just round trips of a few miles. Then when traveling about 6.5 miles to mechanics, the last mile or so the truck started to run rough and felt as if it would stall at a light. Left it with mechanic and he had it idling in lot a few times over course of a few days but could not reproduce problem. Told him the truck needed to be driven I think to reproduce rough running.
Now by running 2.5-3 miles to nearby park, spend an hour or so at park, and then within 1/2 mile of return trip the truck will start to run rough.
Seems like it will run fine for up to 3-5 miles steady idle/good acceleration, but then all of a sudden it will start to idle rough/run rough/sluggish accelerator response.
Thanks in advance for assistance.

in2pro

Welcome to the forum...
What is the engine temp doing, is it in range?
How about the condition of the catalyst?

NJ_Tahoe

Thanks for the welcome and the reply.
Engine temp seems normal. Doesn't appear to be running hot.
Planning on taking another run with it later today and will pay close attention to see
if it is running above normal. I have looked at gauges in the and didn't notice anything unusual.
You know, I saw some other info regarding the catalyst on other threads.
There was mention that the catalyst could become plugged/clogged by fuel mixture running too rich for too long.
How can the catalyst be checked?? Is there a procedure I could perform??
I saw some info about checking the force of the exhaust at the tail pipe. I actually took a look at this yesterday and the exhaust when revving engine seemd to blow out 3-5 feet by looking at lawn that needs to be mowed. Not very scientific, but I took a look anyway.
There were some other posts that mentioned the catalyst would glow if it was plugged/clogged and got super hot. Probably something better checked at night.
Thanks again for your help.