Im guessing FSM stands for factory service manual. I was lucky enough to come accross one on ebay awhile back for about 30 bucks.

My truck is a 92 but im sure most things are similar so if you have something specific to look up let me know and I can check it out

 

I notice that it behaves better when I let it warm up, as well. No smog testing in Louisiana, so no G2P sold here.

 

How clean is the inside of you throttle body and intake? Have you run any fuel system cleaners through it? If the throttle body is not real clean, clean it. Also you can run some cleaner through a vacuum line to clean your intake and valves good. To do this you need a long hose that will plug into your intake as high on it as you can and step it down to as small a hose as you can or use some kind of valve to adj. the flow so it does not get to much cleaner at one time. I use just some cheap fuel injector cleaner. Put the hose in the bottle and start the motor. Let it run until the bottle is empty. Then, turn the motor off and hook you vacuum line back up. Let it set for about 5 mins. and then restart the motor. The set time will let the cleaner soak into the build up that did not come off easy. When you start the motor back up it idle rough. If you can drive it around a little to clear out what cleaner is left in the motor(when you take off, hold it to the floor until it changes into 2nd) or you can just rave the motor up and hold the RPMs up some but not real high. It will smoke while you are doing this. Do not worry, this is normal. Also, put 2 bottles of cleaner in your gas tank to make it strong. I buy the cleaner that is at the Dollar Tree cause it works for what I am doing and it is cheap. I am not saying that this will fix your problem but, it can and will make most vehicles run and perform better. Hope this helps if you try it. I do this once a year to all my vehicles like a day or two before I do a tune-up.

 

I did put some fuel system cleaner in the tank and ran the truck a good bit (fuel mileage is awful-- I went about 100 miles and have burned 1/2 a tank). We'll see if it helps.

The issue seems to be that the injectors are sputtering on tip-in. I pulled the air cleaner off and operated the throttle by hand to observe this myself. The question is "why?"

 

Your injectors could be dirty and causing all this. New injectors could solve this problem. Dirty injectors can cause you to get bad fuel mileage and the truck to have performance problems. I say dirty that also means that it could have a build up in it. There is a system made that cleans the injectors but, it is hard to find any more. The way it worked was you removed the power to your fuel pump. You then hooked a line into your fuel line with cleaner in it that was pressurized. You started the vehicle and run it until it cut off. Then you hooked everything back up and drove the vehicle to check the operation of everything. I have used one before and it worked very well. It was SMP Ultra Cleen Fuel System Cleaner. It was at the dealer ship that my dad worked at. Oh well, hope some of this helps you out.