Spits and stutters while under a load?

Just got the vehicle listed above, the man told me he put in a new fuel pump. It was running fine until I stopped and got gas, then it ran fine for about 20 miles, then it started to spit and stutter while in drive would not go above 20 MPH. Put it in park runs fine put in neutral runs fine. I have changed tb, vvt, cam sensor, crank sensor, the sensor between air filter and tb plugs manifold gasket put Heet and Seafoam in tank, but still have the same symptom spit sputtering while under a load. No codes, no SES light. Any advice would be helpful and appreciate.