WTF is wrong with my Auto?

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This past Friday late afternoon I was leaving Port St. Lucie (1.5 hrs North) and was headed down to Davie to hang out at the Tower Shops our local 52 week Friday night cruise-in with over 300 Plus cars now from early models to late models.

Anyway, I'm cruising along doing 80-85 MPH during the 1st hour and truly enjoying the ride. Then as the odometer hit 62,000 miles my car was jumping 1000 RPMs and shifting out of overdrive by itself and would then come back down again in the Revs. At first it only did it twice and was fine for about 10 minutes and then it started doing it again. Now I arrived and I parked the car like always next to another 20 Stangs....this Friday there were more late Models that I can remember. I said to my friends let's see if she acts up on the way home.

4 hours later, I call it a night and start my ride back home to Port St. Lucie figuring in the 1.5 hrs to get home I should have plenty of time to see if it happens again. Well as soon as I got on the highway she started jumping by itself out of overdrive by 1000 RPMs and would shift itself back down but this time it was much worse and almost relentless. I finally took the car out of overdrive and drove it in drive and it would do the same thing but not as bad or often.

WTF is wrong.....I hope at 62,000 miles I don't have to replace a tranny or stall converter. I had 232,000 miles on the original tranny on my '86 Olds 442 which I bought new. I have a transmission cooler. A couple of friends think that because I went to 18s (285/35ZR18) all around that I may of messed up the tranny? About 3 months ago I put in long tube headers and got the MIL eliminator extensions....I already had the MIL eliminators 3 or 4 yrs ago when I put in my Pro-Chamber and never had a problem. The check engine light didn't come on but then again I don't believe it would since this looks tranny related. I've always babied the car although I do drive fast...typically 15-20 miles over the speed limit. Once in a while I stomp on the car to see if she can spin the tires but only when it's a fairly cool day in our winters. Then there was a period 2 yrs ago when I went weekly to Moroso to drag race and would just stomp on the pedal on the last yellow light on the tree. I did that for 3 months and then replaced a seal which I noticed went bad after leaving a small puddle of tranny fluid. I have had the tranny serviced for a new filter and fluid some 20,000 miles ago.

Has anyone experienced what I've mentioned and what was the end result and cost. Could there be a sensor like on a GM tranny that may be bad and a lot cheaper to replace?

Appreciate the info!
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