I have a 1987 Chevy automatic 1 ton pu. When leaving from a stopped position it goes through all gear motions except the last one keeps running high we changed transmission fluild and filter but still will not complete the final shift.

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see this vdio

Is the security light flashn after it dies?prob Pass lock. Google s10 pass lock...... Check your pump by clamping return fuel line an if it helps your fuel presssure low. May needa pump.
If I'm not mistaken it takes more pressure to crank than to run.

Because you BCM knows that the motor is not the original so you might need to visit your local dealer to have it reprogrammed

ENG 1 - 20 amp fuse - under hood fuse Box . This fuse powers the O2 sensors heater circuits , Emission - purge an vent solenoids , mass air flow sensor , camshaft position sensor an A.I.R. intake recirculation relay - if your vehicle has it , L31 only
I would look for wires for o2 sensor melted on a exhaust pipe or manifold . Isn't your check engine light on ?

the 203 transfer case is operated by a metal chain/belt. the 205 is all gear driven.(lasts longer than 203) most 1/2 ton chevy trucks have the 203 if they have the automatic. some of the newer ones have the 208. hope this helps.

1978 Chevrolet Truck C10 1/2 ton P/U 2WD 4.1L 1BL 6cyl



Fig. 14: Vacuum hose schematic - 1978 250 engine, light duty emissions (except California)



Fig. 15: Vacuum hose schematic - 1978 250 engine, light duty emissions (California)


Hope helps (remember to rate this answer).

key on engine off, depress gas to floor pedal three times and key off

check the intake manifold for vacumn leaks also check all hoses and lines to it as well as the map sensor being weak

The transmission is worn. The cheapest fix is changing to a high quality synthetic fluid. This will allow for easier shifting when it is cold.