Sounds really similar to what mine did 66RFE at approx 50k mi. Mine resulted in a full trans replacement including torque converter.
It just sounds similar, doesn't mean it is. I heard a pretty good Ka-thunk, I thought I hit something in the road surface going up to speed from on ramp to interstate, So under acceleration also.
Fkn thing never through a code, middle of the night, I made it another 60 mi home in 4th gear limp-mode just fine. When I got home I checked the tranny fluid - level and smell all seemed fine, two days later drove it to the dealer 20 ish miles away. No longer in limp, shifting harshly but going through all gears, I didn't 'test' it or anything, just wanted to get there.
They told me it was smoked and needed a new trans. Service guy stammered something about rebuilding the trans but neither of us wanted him to have to follow through with that.
Mine also had precursor to failure for several months, even longer and that an occasional 'delayed engagement'.
I referred to it as slipping but I was incorrect. From a stop the trans would experience delayed engagement until 1200 to 1500 rpm on occasion. Hot stop and go traffic. I had the dealership evaluate the situation prior to the failure, they drove it around their parking lot and said couldn't replicate the problem, no action taken. I let em off because I wanted to think my truck was ok, me so dumb!
Any way, I think you may want to expect the worst but I'll hope for the best.
For the worst - $5500 out the door, torque converter and all. It chapped many parts of me, fo sho.
Dealer also said my fluid was burnt as hell smelling. I argued told him that was one of the only things I knew to check and it smelt fine, synthetic but no burnt smell.
He and I didn't get along.
I do hope for the best, but even if limp mode clears I wouldn't stray to far in it without a planB. Me being cautious.
I have read of several others with the same or similar issues. Some member made a pretty funny crack about the "..Power Wagon sitting in the corner munching on tranny's".
It was hard not to chuckle, it just burned a little inside when I did.
I'm actually pretty bummed I bought a second 66RFE. I wish I would have slowed my roll a little and investigated what other options may have been available, maybe none, but I will not buy another RFE transmission. If mine fails again I will fit a new 8-speed under it, hopefully, no matter what kind of effort is required.
5.13 gearing with an 8 speed, lol sounds like fun until I'm replacing $2000 worth of sneakers.
Good luck with it, hope yours is different.
'16 PWagon with a badass Greene tune feed'n & Fire'n 6.4L 6spd // 5.13 AAM // 37" KM3, -24mm // DOR, Purple Cranium // CAI, ARH, Solo Mach44 // z36, EBC // Custom Graphics, AVS, 4% VLT // Morimoto, Rigid, Diode Dynamics // Alfa, Diablo //.................
