The TBI system on the GM truck is very good but it does have a few problems that occur at some point on them all.

EGR Stacking
The symptom is a slight tip in hesitation on light throttle. Also after a extended light throttle cruise the engine will stall or idle rough when pulling up to a stop. The symptom will clear its self if you leave your foot off the throttle. The cause is the EGR valve and Solenoid. The bleed filter on the solenoid is foam and it disintegrates with time allowing dirt to enter the bleed. The EGR Valve itself has a back pressure sensing metering function and with age and carbon it caused the valve to open to far. The test is simple. Warm up the engine, run it at a light cruise and check the valve by placing a gloved finger on the diaphram (it will be hot) The valve should flutter. If it's pulling all the way open its failed. This causes two things to happen. The manifold vacuum drops causing the computer to command full rich, but the high egr flow has no oxygen in it so the rich mixture doesn't burn. The fix is simple. Replace the egr valve and solenoid. I recommend the OEM. It's calibrated and clocked way better than any aftermarket.

Bad ECM Ground
The ground for the ecm is attached to the thermostat housing bolt. The wire is a loop with two or three black wires in it. The dissimular metals of the thermostat bolt and intake manifold make for electrolysis and an eventual bad connection. To test for this perform voltage drop across the connector to the negative on the battery. Anything less than .5 volts and the connection is bad. Test it with the circuit loaded. Engine running is best. A good connection will be .01 or more. If you don't know how to do a voltage drop just attach a test lead from the battery negative to the loop and test drive it. The symptoms range from stalling, check engine light with random codes, low power, hesitation or rich condition and sooty exhaust.

Low Power Low Fuel Pressure
When the engine starts getting old and weak problem is worse. The PCV ports in the TBI unit get plugged with carbon. Then the crankcase doesn't vent. The blow by is blown from the drivers side valve cover up the tube and dumped right out on the TBI regulator. This causes the spring to brake a few coils off and lower the pressure. The fix is pull the TBI unit and clean out the passages. Install a new PCV valve and TBI spring. (Springs are available at the mrinjector parts store or ebay store)

Purchase a spring here
 
Service Manual's 03/20/2010
 
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