1992 V6 Toyota Pickup

I deliver mail and my truck just kills on me. I can usually go about 2-3 hours then at one point it starts sounding like it isn't getting the juice ( like a sputter over and over till it kills) it needs to keep idiling and just dies. Start the truck and go hoping it doesn't happen again right! I have brought it in to Toyota place 3 times now they have cleaned the system? changed spark plugs, wires and carb., also O2 sensor and nothing insisting each time it is fixed. Nope I have also told them how when I start going in between 10-20 mph my truck doesn't want to shift and nothing is done about that either! Any help would really be appreciated! Oh and they have put it on the MACHINE LOL Nothing shows