I have a 79 Dodge truck that isn't getting any fuel to the carb but the fuel pump works. I can only assume there is something wrong with the sending unit. Any ideas?

Also, when I bought the truck it ran just fine. Got the truck home and he keeps wanting to run off what sounds like 6 cylinders (v8 truck). There was only one time after doing a compression test that it ran strong and sounded good. An hour later I went to drive it and it was back to the 6 cylinder feeling. Any ideas? I have even went so far as to put a points distributor in it to get rid of all electronics to see if it would help and no it did not. Thanks guys