I have a 87 with a F.I. 302 5.0. I can start it up fine and it will throttle up fine while its not in gear. When I put it in gear under a load it spits and sputters and backfires through the intake. I have tested or changed the following: T.P.S., Map sensor, new msd distributor and coil, fuel pump and filter. Its getting spark and fuel. Checked the injectors with a light and they all work. Set the timing and am still having the problem. Any help will be greatly appreciated

 

I would check for vacuum leaks. Use carb and choke cleaner and with your truck running, spray all vacuum hoses and fittings. If the idle increases when you spray an area, then you've found a leak. Don't forget to follow lines outside the engine bay. Not sure, but there might be a vacuum modulator on your transmission as well.