1990 Toyota Pickup Jerks

I have a 1990 4x4 with a 22RE engine. When I go down the road it shuts off and back on and jerks very hard, hard eniugh that I think it has streched the timing chain before it should be changed and has gone through a U jount Bad and Quick. If you keep you foot in the gas it will continue to jerk bad however if you turn the key off and back on it is like it is reseting something and its ok for a while. I would think its something electrical but if I have a full tank of gas it wont do it as much and it takes it maybe 30 miles to start and once reset it doesent do it as quick. Once the fule level starts dropping it does it more often and if it is below a 1/4 tank it does it every 2 to 4 miles. We have tried changing a lot of things, computer, all plugs and wires, tried another dietrubuter, put a fuel pump but I wonder if its bad, changed some relays and so and so. I am ready to have to put new timing chain and all on and I hope you can help me with the jerking. Dont want to put another timimg chain in before I have to again.