Hi I'm back I have 1976 Chevy C20 pickup I was wondering if anyone knows what transmission came in it thanks

faulty reverse light switch on gear nox

If the starter and solenoid is good and not hanging up I would check the Ignition switch to make sure it is releasing back after turning it to the start position. Be sure key is not sticking.

the level of oil in a manual transmission has little bearing in the shift operation of the transmission as all it does is lubricate the working parts
excessive oil will overload the input shaft seal and may cause oil getting to the clutch plate or leaking out of the drive shaft seal
However the quality of oil used will have a bearing on the shifting of the gears
If the oil is too heavy ( viscosity above 80 oep) it affects the ability of the synchro mechanisms to work especially in fast shifting requirements
if it is too low ( 30 or less) it affects the wear or the gears and bearings and again will not have the shear strength to allow the synchros to engage properly with out causing excessive wear
From your question and problem description, I suspect that the problem is not in the transmission or oil level but in the clutch operation
If the clutch plate is not properly disengaging, the engine revolutions will not allow the synchros of the gears to operate properly and make shifting near impossible
so check the oil used and the level and fill to the level specified by the manufacturer
check and adjust the clutch for correct operation as there may be a problem in the slave cylinder/ master cylinder / cable operation that is not allowing complete disengagement of the cluch

check for vacuum leak for the idle or idle mixture screws settings
no power in 3rd gear can be low fuel level, filter problems , ignition timing ( static is 12 degrees BTDC idle )
more than likely a vacuum hose missing after assembly

The simple answer is yes! To both! A blown head gasket will cause a lack of compression and either a black or white exhaust emmision. Improper intake manifold seal will cause rough idle or high idle.

Hi
You need to remove and clean with a carb cleaning product the carburettor and air blow it
Catalin

Vacuum Diagrams - AutoZone

www.autozone.com/repairinfo/.../repairGuideContent.jsp?page...

AutoZoneGM Chevy Mid-Size Cars 1964-1988 Repair Guide ... Fig. Fig. 4: 1971 V8 enginevacuum hoses ... Fig. Fig. 12: 1976 350 V8 engine-4bbl with EFE and AIR injection systems .... Fig. Fig. 52: 1980 5.7L V8 engine-automatic transmission federal. images for 1988 Chevy V8 5.7L 350 4bbl vacuum ...

if all other gears work fine then it's just a matter of changing out the solenoid that controls that gear you will save quite a bit of cash you don't have to change the whole transmission