s-15 pickup-lack of power-uneven acceleration

just bought a pickup for a third vehicle to help with yard stuff. only problem i have is it has uneven acceleration seems to start out ok then has a slight jump. i'v notice it has a signifigant loss of power especially noticable at freeway speeds...it takes forever to get up to speed and will loose speed on even slight inclines. my father in-law put on a spare carburator he had since he thought that was the problem and even though it helped i stiil noticed the same problems. he did find and fix one small vacuum leak before the new carb but other than that the only i can think of is maybe it needs a new cap and rotor? too much lack of power for a v6 can you help??
thanks
Rob ([email protected])

Please..........give us the year and engine size.

The problems with an EFI engine are very different from a carb engine.

Since you mention carb, lets assume its from the 80's.
I would suggest your ignition timing is retarded.
1. It might be the static timing, although this provide a rough idle.

2. Either the vacuum or centrifugal advance is not working or you have the vacuum advance hooked up to a manifold source. It should be ported vacuum.

Sometimes, you will find a thermal vacuum switch mounted on the intake manifold which provides manifold vacuum advance when cold and switches to ported when warm. These are notorious for getting stuck on manifold vac only. Just bypass it and run ported vac all the time.