I kept experiencing intermittent misfires while driving. Thought it was the fuel pressure but it checked out ok, 55psi. I had replaced the plugs, wires, rotor, distributor cap, crankshaft position sensor, ignition module and ignition coil. I checked the spark on each cylinder and determined that #1 was the problem.
I removed the distributor cap and when I grabbed the rotor, it wobbled. I pulled the distributor & determined that the plastic top bushing was badly worn causing the reluctor to rub on the hall pickup device. The distributor is plastic and has no means of oiling the internal built in bushings. I replaced the distributor with another unit, but first took it apart and applied cam lube to the shaft and bushings. I also replaced the Hall device as it had rub marks on it. I never had any DTC's set and this must have been the problem as the truck now runs fine.

 

did you re do camshaft retard learning function after distributor?

 

No I did not do a camshaft retard as the shop manual says that there is no need as the computer (ECM) controls the timing. The distributor cannot be rotated as the forks on the distributor housing fit tight on the upright dowel pin on the engine case.