My 89 gmc sierra surges when idoling on in drive i dont know where to start....

Check your fuel relay.

Oxygen sensor on exhaust. Mass airflow sensor. Air/ idle control sensor. Throttle position sensor

Without testing we'd only be guessing ! Do you want to replace a bunch of parts till the problem is fixed ? Hooking up a scanner an looking at engine management system sensor's (data ) inputs to the engine computer would be the first place to start. If you don't have the ability to do this , suggest you take it to a qualified repair shop . Or learn automotive Engine system diagnostic's . A lot of thing's could cause the problem your having . Do you know how to test automotive electrical an electronic system's ?

Basic Ignition Description Operation and Testing any car

Electric Testing Techniques You Need to Know
ECM Inputs and Outputs Diagnosis

coulb be a vacuum leak at the intake, any codes set( eng light on?) follow them if so

broken trans mount possibly doing that

if u own a 1989 sierra u dont have an obd or obd ll computer on board if high idle all time then search for a possible vacuum leak and or throttle/carb needs adjustment

If all your other gauges work, more than likely you have a bad sending unit in the gas tank or bad ground to the sending unit.

Sounds like you may have broken your timing chain. Try doing a compression test. You should get pressures no less than 90-100 psi. If you find extremely low pressures,you probably lost the chain. This could have caused valve train problems. Good luck

if it has a 4.3 liter motor a 86 to a 97 if it has a 350 motor a 81 to a 96 will work hope this helps

there is an ignition module located rite beside the distributor cap on the distributor base these are well known for getting weak and heating up thus causing your engine to stall.