4.3 V6 full-size poor performance

93 Chevy 1/2 ton WT with 4.3 V6, automatic. 81K miles. excellent condition and maintenance.
I know it's never going to be a tire smoker, but I owned a similar
truck years ago (recently bought this one) with a lot more miles that ran better.
Truck runs nice and smooth. Internally, engine is in good condition.
I had my reliable independent mechanic try to fix the driveability problem to no avail. So far...new plugs, cap and wires, everything checks to specs on diagnostic machinery. FI serviced, engine de-carboned (apparently some old GM TSB). New fuel filter. Has new K&N air filter. Truck is still a dog on the freeway, especially with the AC on. In fact, it is so gutless I am afraid to pass anybody if it requires me to go more than 70MPH. It also has what I consider poor throttle response off idle. If I drive it like I stole it it's OK but at low throttle it stumbles. At full throttle it seems to run fine all the way up through the gears. In normal driving it sort of feels like the timing is not correct, especially at higher RPMs. With the AC on it seems to lose all desire to pull. The slightest incline will cause it to slow down dramatically and start hunting for another gear.
Any ideas? I hate to take it to a dealer or another mechanic but I'm close to doing so.
TIA
Mike
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Well being a 93 that rules out a flat cam. It should have a roller cam. I would look at the exhaust system and the fuel system. Catalytic converter might be getting plugged up. Injectors might not be up to par. These engines are fuel pressure sensitive. Under 12 lbs and they will have minor drivability problems.

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thanks for those tips. both check out OK. Have also checked O-sensor, timing. nothing seems to make it any better.
any other ideas?
thanks
On Tue, 01 Jul 2003 11:56:32 GMT, "noname"

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