If im cruising down the street and just stick at a constant speed the truck will jump like forward and backwards. And motor will run weird. Its a 1991 toyota pickup with 22re in it manual 5 speed. Help please. I dont know if its the tranny or motor

 

What about if you run the truck in the neutral and slowly give it throttle or hold the same RPM where you experience the problem when driving, do you have any rough running or does it run smooth?

Based on your description it's probably the engine, one of three things, ignition, fuel, or compression. You can probably rule out compression striaght away, unless you have obvious signs like water in the crank case, new inspection ports in the block, or funky smoke from the exhaust.

Have you checked the ignition timing? Have you checked the distributor cap/rotor for excessive wear? What about the plugs maybe there is a broken electrode on a spark plug or something. Have you checked the valve clearances? Go through the factory service manual standard mateinance/tune up items and see if you turn anything up in the process.

If the jumping is violent like the engine is cutting in and out, based on my experience I would suspect a fueling issue. You can try replacing the fuel filter it's cheap and easy, well mildly annoying due to the location under the intake. It could also be the pickup sock on the pump itself (in tank), or a bad injector or something like that. There may also be procedures in the FSM for testing the pump and making sure you have good fuel pressure.

 

run weird how? kinda does sound like fuel pressure...ie, failing pump. more detail needed, though

 

Surge and bucks, kind of like a spring loading and unloading? That is axel wrap.

Likely causes are a leaf failed, look for cracks ect.