car cuts off , and studders at moderate speed

i have a 1988 buick cenury, and it was running fine till two days ago, then it ran hot and quit. i found that the thermostat was locked closed. I replaced it and no more overheating...but now it studders at moderate
speeds... ( between 40-50 mph) and it also has a serious miss in the engine, that was'nt there before it oerheated... aned it cuts off when i come to a stop after doing 30mph or better
PLEASE HELP!!!!!!!!!!!
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Better check for head gaskets, pull the plugs and look for signs of coolant, feels like a misfire? any excess vapor out of the exhaust, leave any vacuum hoses off when doing the repair? 2.8 engine?

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