Please Help!! Engine Problems

[thisolechevy]

Please help me!! my engine is running bad I had problems with the timing but I think I got it fixed, My truck runs great!! Until about 50mph and then it starts to "jolt" it seems like the engine is about to die, and then catches up again and the tach. doesnt show rpm change??
at first it started to back fire and spit around 45mph so I advanced the timing a wee bit and it got better and better, but now it just "like I said JOLTS" and tops out aroung 53-55mph and I know that is not its full potential. What to do?? Do I just take it to a mechanic or is there something simple I am missing??
Also I have never had the vacum advance hooked on the dizzy, should I hook it up? would it solve at least some of this? What am I missing?????
Please help I want to just sell the truck now! but I know I would regret it for years to come.