i have a 1999 4.2 f150 i recently put in a new transmission and everything seemed great until a few weeks later i noticed my truck idling rough and sometimes shutting off. but it seems the worst when im at a red light and the truck bucks and wants to take off, but when i hold the brakes it shuts off so i have to put it in neutral to keep it from doing so. does any one know what this problem might be?

 

Check your in drive idle RPM.

 

you may want to clean/replace your idle air control valve as well.

 

Clean it with Carb/Brake cleaner and then hit it with some WD-40...