poor acceleration, bucks at constant speed

I own a 1998 2.2L S10 (~130,000miles.)

A _slightly_ rough idle has been present for many months. Within the last two weeks - power/performance dropped rapidly (still idles OK). Now, vehicle is really sluggish, won't accelerate much past 3500rpm, and bucks badly at constant speed - 35mph/3rd - bucking stops if I step on accelerator. Bucking is worse in lower gears. Battery is fine. Fuel filter is new. Only engine code was AirIntakeTemp sensor (P0113) high - which I probably caused by forgetting to reconnect. Spark plugs must have at least 40k on them.

I've purchased new plugs after reading other threads, but because the problem worsened so quickly, and because it doesn't run rough (like non-uniformity between cylinders/plugs/injectors), I doubt the new plugs will solve problem. It seems like a problem affecting all cylinders. They want to sell me a fuel-pressure guage at autozone... and I'm tempted.

Any help/insight would be appreciated

probably not a bad idea for the fuel pressure guage

I know that you should have a computer code for these but it could also be an oxygen sensor, or a pluged PVC valve.

you can test the PVC valve by simply taking it off, and blowing through it, and I would think that you can test the Oxygen Sensor with a multi meter, but someone else on this site will probably tell you for sure

Thanks for the reply. Will check pcv-valve at next opportunity (code or no).

Update:
Convinced myself it was probably a clogged "cat". Banged cat with hand and found a rattle - explains a vague rattle occasionally heard between shifts. However, "Jimmy" the honest muffler guy, said (on phone) to consider fuel-pump or gummed-up air-intake.

Too many science projects. Went to the mechanic I've been using, watched as he connected a digital psi-meter to the fuel-line test-fitting (under hood). It read 39psi at idle and, when he raced motor, didn't increase, in fact, it seemed to drop 1/2 psi. Mechanic checked meter (hit a button, displayed 37.5psi), acted like nothing conclusive had happened. Not knowing what was supposed to happen w/meter, I left truck there for further diagnostics.

Local autOzone wants ~$250 for f-pump. I could probably install it (remove truck-bed) myself.

Follow-up, for posterity:

Cause of poor acceleration, bucking, limited rpm:
clogged catalytic converter (*CA, USA owners see note below)

Mechanic re-did f-pump tests and found uneven peaks at 48 and 58psi. He said fuel-pump _might_ be on its way, but there was definately excessive exhaust back-pressure. He recommended a muffler shop for/to replace cat. ($80 US for diagnosis)

I visited "Jimmy" who (using acetylene torch) punched 1/8" holes before and after cat. With car on rack and idling, he encouraged me to see/feel the difference in venting-pressure, said it should be the same, it clearly wasn't. Jimmy warned that a converter could/should last much longer and if something caused stock/orig. cat to clog, it might also cause a new cat to clog quickly. No charge.

*CA S10 Owners:
According to both muffler shops, at this time, there is no CA EPA approved after-market catalytic converter available for the 1998 2.2L S10, however, the shop my mechanic recommended said the cat available for the V6 worked (though, the proof will come next smog-check). They pulled a brand-new cat (not reconditioned) out of a box and showed it to me. Dealer wants ~$550 (US list) for new cat. Shop will replace with V6 version for $350.

In spite of relative lack of input from AF gods (still, thanks OverBoardProject) this is a great forum. Sincere apologies for any posting transgressions. Kudos to all.

if the muffler shop is gonna charge $350 just for the cat you should be able to get one from like autozone or something for like $250