90 Mustang loses power in 3rd.
 

I have a 1990 5.0 LX conv. (anniv. ed). I replaced the plugs, wires, cap and rotor. Went to drive it and it runs fine through 1st and 2nd, as soon as it shifts to 3rd the engine misfires, bucks and loses power. I've checked gapping, firing order (2x's) and looked for any loose wires or conections that may have slipped off, no luck. Any ideas?

Was the problem occurring before your tune-up or after? I had a problem similar to yours a couple weeks ago. It ended up being one of my plugs was malfunctioning(recently tuned up in Aug.) I replaced it and everything was fine. Also, as a suggestion, I would clean your MAF, although I do not think that is the problem.

Nope, it's a new problem
 

I changed everything because occasionally it would misfire if the rpm got too low (felt like it just needed the tune up). With the new stuff, the second it hits 3rd it almost stalls out. I have checked all of the contacts and connections thinking I may have loosened one or knocked it off, no luck. I'm stumped.

is it a stick or auto?

Auto
 

It's an auto...I was thinking torque conv. but it seems too coincidental.

When the car hits third, do the rpms drop as if hitting a wall and it seems like the car want to die, but then regains itself, if that makes sense? Your problem seems to be ignition/fuel related. I doubt the tranny has anything to do with your problem. If you can try and pull codes. This will give you your best bet. If the codes indicate, lean bank(left or right) then my bet would be on the dizzy or coil. However, if the codes pull up a CYL #, then you may have a bad plug or wire.

none
 

Hitting the wall is exactly what it feels like but it doesn't seem to recover. I'll trailer it over to a shop to check codes on it, there's no OBD slot and my diagnostic equipment is a bit limited. I had someone else mention a posisble timing advance or some vac. advance line. I'll update if I can find anything.