What are some of the miles on transmissions? Did anyone get over 250k on the orig? Any tricks to keep it going?

 

Keeping them going:
Install a filter in the line to the cooler: https://magnefinefilters.com/main.sc
There are two main makers of inline filters, Magnefine and Filtran; you'll see these under several labels.
(After a transmission failure a filter is usually installed in the line out of the cooler. This is to catch debris bits that lodged in the cooler. If there's no debris, the hot fluid to the cooler filters better than cool fluid.)
By the way, on cars with hydraulic power steering, one of these filters, probably 1/2" size, in the return line to the reservoir will keep the power steering system running longer. All hydraulic systems need clean fluid.

Keep the fluid fresh and good. Plan on a fluid replacement schedule. Modern fluids are probably good for 100,000 miles. Do a full flush and replacement before this, or do a partial drain and refill say every 30 or 40k. It's best to use a fluid that "meets or exceeds" the specs for that transmission. Be skeptical of fluids "recommended" for the transmission. These don't meet the spec...maybe they just haven't be tested (sometimes at a high cost) for compatibility...sometimes they are close to the spec but not exactly meeting it.

Never, ever, change directions while rolling. Never shift to drive while rolling back, and never shift to reverse while rolling forward.

 

And, if you tow much, install an air-cooled transmission fluid cooler in front of the radiator.

 

I have the extra cooler, Ill add a filter. Hoping to get 300k.