Hello all I just bought a 81 ranger and im having some issues with it, when i put it in gear it will stall i just replaced the fuel pump on it but im not sure what it could be.

 

Welcome to the forum

You have an F-150 or F-250 with Ranger trim package, which is quite a bit different than 1983 to 2012 Ranger models, they were smaller pickups than the F-series.
So your "Ranger" is like a color or chrome bumper, doesn't designate anything mechanical about engine trans or truck.
Like saying I have a 1981 Red Ford truck with 6.6l that stalls when I put it in gear, "red" and "Ranger" would be interchangeable in 1981

Yours is a 7th generation F-series 1980 to 1986
6.6l 400ci gasoline engine with carburetor

My best guess would be choke is not set right, or not working
Assuming an automatic transmission, from the "put in gear" statement, if you lug a cold engine it WILL stall.
Choke does two things, it creates a Rich fuel mix that a cold engine needs, and it bumps up the idle so engine won't stall under load at idle.
Generally automatics need idle RPMs above 750 when warm and above 850 when cold or they will stall in gear

 

I would start with a tune up, unless that's been done already (plugs, wires, distributor cap & rotor) Then set the ignition timing (12*BTDC) Next if the timing setting doesn't fix the stalling, adjust the idle speed setting to around 600rpms cold. If there's still a stumble, check the freeplay in the accelerator pump linkage, should be zero freeplay there. When the throttle linkage moves, you should get fuel squirted out of the pump nozzles in the throttle bores.