Need help with the 3.7L

Sounds just like my 69 Dart on a cross-country drive in 1991. It would start stumbling around 55 mph on a flat highway, especially when warmer outside. The fuel hose at the fuel pump inlet was soft and collapsing. That was about when they started adding ethanol everywhere. I replaced it in NM and purred the rest of the way to CA. Change all your hoses to the better "fuel injection" type (you can find the SAE number in a search). It is much stiffer and ethanol doesn't attack it. Don't fool with old spools of "carburetor hose" out there.

If that doesn't work, try blowing air back thru the gas line (remove gas cap first). There could be crud on the pickup sock, if it is even still there (usually not). Next step, remove it and see, or just replace if erratic output since only $45 on ebay (a few tricks, read here first).