88 Burb, runs rough at start, gets worse

[kw]

Hey all,

I'm trying to troubleshoot a problem I'm having with my 88 GMC suburban.

When it starts, the idle is rough, when I start to drive it sometimes backfires, but runs rough and seems to lack power. If I romp on the gas it seems to get up and go OK, but when at around 45-55 mph it seems to hesitate and run rough. I checked the plugs and they seem OK. Thinking it might be water in the fuel, I've been running drygas and fuel injection cleaner every tank and still it does it.

I don't have a shop manual for it yet, and was wondring if there is a systematic approach to repair this without replacing every sensor in the vehicle. Any ideas?

The engine is fuel injected and stock. 94k miles.

I was going to start with the fuel filter. Where is it located?

Thanks in advance for any help.

Kurt