I smelled the dipstick recently when checking the transmission fluid, and it smelled burned. Thus, I don’t think I should do a flush; just drain the pan, replace the filter and pan gasket, and refill to capacity (4-6 quarts of Dex/Merc). Doing a flush would be more likely to cause problems with what has probably been a neglected transmission (though I do have a receipt for a rebuild about ten years ago).
2 gallons Wal-Mart Super Tech Dex/Merc $11.48 each = $22.96
AutoZone Duralast filter/gasket kit $9.99
NP241, 2.15 quarts of the same Wal-Mart Super Tech Dex/Merc ATF.
75w-90, synthetic if possible
80w-90, synthetic if possible
Already done (I went through so much coolant while changing the hoses and water pump that the entire system got flushed and refilled several times).
Suck it out with a turkey baster, replace with new fluid, then bleed the brakes (if possible — they may be too rusted to do so).
Power steering fluid:
Also suck out with a turkey baster and refill.