this is a very common problem, your throttle is probably just getting stuck, which means on the side of the carburator the throttle cable hooks on to it, and either the spring could be bad and worn, the throttle could just be dirty and covered in grime ect. just get out and buy some carburator cleaner in the aerosol can and spray the throttle really well, and if it still happens it probably your spring but you can tell just by moving the throttle from the engine to see whats going on. also while your driving your truck and it starts to rev really loud and suck and sticks as your explaining simply put your foot under the gas pedal and lift up on it, thats all it'll take to stop it, make sure if it happens again don't let your engine scream like you said it has been do what i said pull the gas pedal up when it does it, these trucks are very prone to spinning bearing ect. anywho i hope i helped if you have anymore questions about it or don't explain, just write me.