Weird #3 cylinder misfire

[gesellman]

This is the weirdest thing I ever came across.
88 Trooper II 4 banger.
I was low one quart of oil, (it has an oil pan leak, one quart per month) so I put in a quart, I forget to put the oil cap back on and drove for 20 miles and it ran just fine.
I stopped at work, backed into a somewhat steep driveway, (nose pointing up) and left it there for about 3 hours. When I went to leave, I started it, it idled fine, but when I went to rev to take off, it started misfiring.
I looked under the hood, and found the oil cap and put it back on, there was only a few specks of oil here and there from the open valve cover, but not a lot.


When I take off and step on it, it goes away, sometimes right into second gear it runs fine until it goes into third.
If Im in first and keep it at a constant rpm, it doesnt misfire.
Nothing too weird yet...
This is the weird part:
When making either a left, or right turn, be it a long or short curve, it runs fine until it goes into a straightaway and runs until I shift into the next gear, then, the misfire comes back....
RPM gauge jumps about 300 - 600 points when at steady run on highway, always up, never below actual RPM's...
WHAT THE *%&$@^&%?????

This is what I've done already.

Cylinder pressure between 90-100 on all cylinders.
Mechanic at a "reputable national auto parts chain", called my truck a "pees of shunk" which I think may mean "piece of junk" in whatever his language may be.
After almost popping him in the mouth, but fearing a lawsuit and a free green card for him on my behalf, I proceeded to go to my local auto parts store and did the following...
Changed plugs, wires, dist. cap and rotor, (or button as the auto parts guy called it)
Took the distributor apart and cleaned it using an electronics spray cleaner.
Took #3 cylinder wire, put a plug in it, and started the truck. I got constant spark without any spaces in between. Just a clean, even spark the whole time.
Fearing a stuck valve, I poured 2 quarts of Marvel mystery oil into the crank case, and have been running it for two days like that, but nothing, it keeps doing the same thing.
Sensors? ground?
If anyone has any ideas I would greatly appreciate any help....

88 Trooper II
4 Cyl.
197,000 miles
Rebuilt at 95,000 miles


Thanks in advance.

[gesellman]

*UPDATE*

In looking around, I saw that this thing has fuel injectors.

How do I test to see if #3 is working properly?

Also, the throttle positioning sensor is right above that injector, when I touch the wire connected to it, I hear a clicking sound somewhere else , and idle goes down.
Could the TPS have anything to do with only one injector?

Any online guide to replacing injectors?

Thx

[gesellman]

Gee... Don't nobody trample over each other to answer my questions...... We gotta be careful we don't overload their servers by all jumping into this thread!!!

Thanks for nothing.