97 Bravada - Sluggish acceleration

Mileage 134,000, just at garage last week for fuel filter change and oil change. Back today for sparkpug replacement and clearing abs codes.

Problem, When accelerating car bogs down. seems ok on city type roads but if need to make an incline really slows down. The other week it actually stuck in gear, wouldn't gear down on a long climb, then the check engine light came on. This light did go off after the 2nd day. On highway drives does not like to accelerate or maintain a constant speed, you need to keep putting the pedal way down to maintain highway speeds then back up when it catches up to speed. Now we picked the car up at the and the check engine light is back on. My boyfriend is returning parts to Autozone tonight and if the light is still on will have them check. The garage ran a test and said all the sensors and electrical stuff is good. This problem, along with my ABS kicking back at me, we had to disconnect the one speed sensor which was just replaced, and the long list of other problems is really costing us alot of money. Any clues where to start looking. My boyfriend is getting tired of putting money into this vehicle.

Thanks a bunch.
Deanna