get one of those 48" zip ties at home depot (in the electrical section). trim the bottom corners in a v up 10 cm. take a ruler and mark every 10mm up to 100mm. start the truck then let it warm up to operating temperature (should be around 165) slide it down the transmission tube and compare it with this graph:
Or for 160 bucks after taxes for a pan drop fluid service or 200 for a full flush, have these guys do it:
Had the mistertransmission do it in ottawa on friday with no issues so far with the wifes commander....