While I go down the highway the car seems to bog down from 55 to 45 and struggles keeping up and slowly creeps back up to 55. It only does this every so often, maybe every 20 miles. The car sat for 11 years and its a modified 350 with flat top pistons and rebuilt 305 HO heads along with a quadrajet 4bbl. I'm wondering if maybe the transmission just needs a good flush since it didnt do this the first 300 miles I drove it. The tranny still shifts fine without hesitation as well. Its an 84 trans am and has the 700r4 in it.

 

Update: It seems to only be doing it at night. When I hit the gas it slows the car down. My car died going about 30 as I pulled into town. You can smell gas while this happens as well. The car seems to try to mildly rev itself up to speed slowly but you have to stay off the pedal to keep the car going. Any ideas?