2000 Chevy Blazer Maybe fuel injector problem?

Hi I have a 2000 Blazer Traiblazer edition with 4.3 automatic four wheel drive with 126000 miles. The problem is when I crank the engine everything is fine but when I go to leave then engine wants to stumble between shifts 1-2 then 3-4 but not drive or over drive. It does not matter weither you let it warm up or not or if it's hot or cold outside it only does it for like 5-8 miles then stops. I thought it might be a Torque converter problem but the engine still stumbles in neutral and park. Also at 60 mph it feels like the TPS is bad by stumbling and hesitating but I checked it and the voltage is correct all the way thru WIO. I have replaced plugs, plug wires, air and fuel filter, cap and rotor, thermostat, and CAT converter. Fuel pressure reads @63 psi thru idle and rev. I just don't have a clue anymore, so maybe you guys can help me please. Thanks Chas