1994 Pontiac Sunbird 3.1 v6 having problems.?

I own a 1994 Pontiac Sunbird with the 3.1 L V6 with the aoutmoatic transmission. My problem i am having is while im driving down the road at about 45/50MPH maybe somewhere in between and am holding the pedel halfway to keep that speed consistent my car starts jerking and chugging i can also hear in the exhaust the chugging/ kinda miss fire like sound.. IDK what this could be and help would be AWESOME!! 2. is while im driving down the road at about 60MPH and its done kicked into overdrive and suddenly i let off the pedle its jerks and it happens after everytime i i let off the pedle at that speed in overdrive. Any bit of help works! THANK YOU!!