Let it idle in Neutral for a while. That get's the pump working, but doesn't load anything. Park doesn't work.
Pump the fluid around a bit, then run it through the gears. Go all the way to low, back up to reverse, one by one, then back to low. Do that several times.
Look underneath for any leakage.
If it's all good:
Leave it in Neutral, wheels chocked, E-brake on, and check the fluid level.
Then, once you determine health, drive it around the block, shut it down, drain the fluid and replace the filter. Adjust the L/R band, and if you have a desire to punish yourself; -only if the transmission wasn't behaving during your drive, adjust the front band.
Otherwise, once the fluid and filter and Low/reverse band are done, run it though the gears a few times, check the fluid level, and drive it like you stole it!
(But look for leaks, and listen and feel for any anomolies during your wanton abandon.)
CJ