Automatic 2000 mustang v6 engine surging at fwy speeds
 

I bought the car with 173,000 miles on it. Automatic 2000 v6. Car now has about 193,000 miles on it. When I first got the car, I preformed all general maintenance because I had no idea if it was ever done. I changed tranny gasket, filter and fluid; I changed the rear end fluid and gasket; I changed the motor oil, changed fuel filter, changed the entire engine cooling system besides heater core; plugs, wires, air filter, surpetine belt, AC kit, ECT... Well, today I noticed tranny fluid on the ground so I placed it in neutral with the engine up to temp, applied psrkipa break and checked the fluid and I ended up needing two quarts. Drove fine but kept leaking. I generally do all the work myself but since I have a broken knee, I can't get under my car. So I took it to a shop, they racked it and I saw the tranny pan gasket was split at a few of the bolts. So, they replaced it with a new filter, lowered it and filled it. It started leaking badly so they lifted it and the owner rechecked the bolts tightening them a tiny but more then grabbed a metal flat punch and tapped around the underside of the pan where the gasket was and it stopped leaking but every time I would stop somewhere, I'd see a little tranny fluid on the ground. Driving home 60 miles at about 60/70 mph, on cruise control, I could feel the engine surge and it would do it for a bit so I let my foot off the gas and it was not doing it as much. This happened to me one other time, engine surging, and is was actually a burnt sparkplug wire. What I'm asking is what could cause this surging? Could it be my transmission? Other than plug wires, what other possible issues could be going on? I recently replaced my TPS sensor twice because engine kinda stalls when coming to a stop by it still kinda stalls but not anything like it did before replacing TPS. What else could be causing that stall when stopping? Also, my car barely started surging like two days ago

Any codes?

As for the transmission leak, I'm afraid that pan's going to have to come off again. The pan's gasket surface could be warped. Or if the new gasket is a plain flat rubber piece (as is commonly packaged with new filters), those are very finicky to seal- OEM gaskets are much better quality, and meant to be reusable.

No codes. Where can i get OEM gasket?

You can still find some on eBay, I think.

There are also some aftermarket manufacturers that offer OE-style gaskets. The material is bonded to a rigid (steel, I think) core, and there are double sealing beads molded into either side of the gasket. Judging by the pictures on RockAuto, the MAHLE W39141, TRANSMAXX 76300EW, and ATP LG204 all appear to be good choices here.

Low transmission fluid level can cause surging.

Next time the pan is off the tranny, have it checked with a straight edge for flatness and also have the tranny's gasket area checked for nicks or gouges. Do no use cork or non reinforced neoprene gaskets, they are trash and usually distort. Use the OEM type with a rigid metal core and the neoprene/rubber/silicone overlay like Urambo mentioned. Make certain the bolts are finger tightened first then torqued to spec in a criss-cross pattern. Do not just tighten them down G-n-tight. You'll just have another leak.