Gear shift drops out of gear then some times willnot come out of gear

I'm not 100% sure on this year, but GM has a Tow haul switch at the end of the shifter in later years if this is engaged it can make your shift pattern weird.

shift sensor in trans bad take the tarns apart . well drop pan n fluid the drop out the valve body then u can see the shift sensor

the best way to fix that problem is replacin the trainy why becayse your problem is the clutchs binside the trainy i will cost you fixing the trainy then replacin i used trainy i am i mecxhanich and i now how much money this problem cost

have you checked that the accelerator cable is moving freely, or that the carb slide is moving freely?

my transmission don't shift stayes on 1 st gear & after 10 minutes I go down by the shifter to let the car go on other wise it will be like nauteral

Stick Shift or Auto? Stick Shift Could be the Clutch. Auto Er................ Torque convertor fault Worn Drive clutches, faulty Valve maze block Or could just be low on transmission fluid but If no leaks Where is It Going??????

Shifting paw or arm is broken in transmission. Very common! Or shifting fork is bent . Both due to hard shifting or abuse..........normally.

could be a faulty solenoid, scan the TCM for faults and drop the sump for contamination

What does the speedometer do when this happens? If it goes dead at the same time you need a Vehicle Speed Sensor which is mounted to the transmission. It tells the ECM what your speed is and without the input from the sensor, the computer assumes the van isn't going very fast and locks in 1st gear.