I have a miss in 3rd cylinder.

What I've seen done to test an injector is to pull it, and swap it for another cylinder. If the miss moves, then the injector is bad. If the miss stays on #5, then the problem isn't the injector.

probly hav a vacuum leak--if run bad at idle--fuel pump cud be failn too--test those 2 plug wires-may b bad inside--inspect distributer cap for inside corrode--w car that age unplug computer then connect again to see if issue clears----the number can mean a worn oxygen sensor-but to confirm u need a diagnostic scan w specific equip--dont go to a dealer or use a code reader

Some testing needs to be done to find the problem. May be spark related (ignition)-check if cylinder 3 has spark. You should see a blue, snapping spark when checking at the end of the spark plug wire-you can buy a cheap calibrated spark tester to check for spark. If spark is good, need to check that injector for #3 is pulsing, so the cylinder is getting gas.
If you find it has spark and getting gas, have a compression test done to see if any mechanical problem with cylinder 3, something like a valve not seating can cause misfires.

After a fill up, the fumes in the gas tank are very concentrated. If problem with evap system, it could cause problems after a fill-up. Just a thought.

put a new coil on it and see if this helps

Unfortunately you have a blown head gasket. The white smoke you are seeing is anifreeze burning.
If it was blue smoke it would be burning oil.
Gasket is in the top of the engine and must be replaced or you will ruin the rest of the motor.
Usually it's a $1800 repair with parts & labour.

If you are missing, due to a cylinder failure, the fuel filter, sending unit and all of that affect all of the engine. If you get a "skip" under a load, you have a cylinder issue. You need to determine what cylinder. Try to throttle it up while applying the brake to keep it from moving in drive to see if you can get it to skip.
If it does, look at spark plugs to see if you can see what cylinder looks different.
Or...while someone is "power braking" and it's missing, remove a spark plug wire one at a time to see if the condition changes. If it doesn't change, that is your bad cylinder.
Then you need to determine if it's fuel, or spark that is the problem.
(Injector bad, or plug, or plug wire.)

ITS NOT A DIESEL TRUCK. You will need extensive work on it, so just take it to a shop.

Or

Supposively it doesn't ruin the engine with small amounts. The tank needs to be flushed, the fuel lines cleaned, fuel filters replaced and the spark plugs cleaned/replaced, cylinders re-oiled and worked a few times in order to get it up and running.

It is probably a bad coil, have someone put it on a computer and see what cylinder is missing. The coils go bad all the time on the 5.4's

NOW VERIFY IF THE INJECTORS ARE FIRING OR CLOGGED OR THE COIL PACK ISNT FIRING.GET A FUEL PRESSURE GUAGE & TEST LIGHT TO HELP YOU OUT.IF YOUR SURE ABOUT THAT TRANS FLUID IN YOUR GAS TANK DEFINATELY CHANGE THE GAS FILTER & PUT SOME FUEL INJECTOR CLEANER IN THE GAS.AFTER YOU FIGURE OUT YOUR PROBLEM.GOOD LUCK