I have a 1996 rodeo that has lost power. It shakes (bucks) mostly from 1st to 3rd gear. It's a 5 speed. When it isn't bucking there's very little power. I'm talking about barely making 30 in a 65mph! I replaced the mass air sensor but didn't help. Fuel injectors and filter are new. I'm thinking it might be the fuel pump....please help! P.S. the volts are going crazy and it's idling up and down.