Engine sputtering at about 65

Sending units are a crap shoot, either they are good or not, when it is out check it with a ohm meter before buying one I believe it is 24-75 ohms full travel. Nos is the best but serious $$$$ if you can find one. I got lucky I found one in a parts store of all places in mine. There is a few threads on them with recommendations just do a search. There are also a bunch of troubleshooting threads on them do it before you order anything can be something really simple like no ground strap on the sending unit to the frame.