If the lines are the same size as the 48RE's and 47RE's then the Acu-temp available from genos would be the way to go. i think they are the best way to go on all dodge trannys. they clamp onto the hot line with no cutting or anything and it gives the most accurate readings. http://www.genosgarage.com/prodinfo.asp?number=ACUTEMP_ADAPTER
What temps are you seeing? It seems like outside temps would affect the readings on this ecspecially up here in the AK. I'm gonna post this up in the 5.9 section to see what people say. I would prefer to actually get the probe in the fluid somehow.
JW
I haven't had a problem with my Acu-temp in the 2 years I've had it driving from Haines to Fairbanks once a year...been down to -60 with the thing and it didn't affect the tranny temp reading... Go for it