[jdmccright]

For the 4L60E transmission, there is a fluid pressure test port located on the driver's side just above and in front of the shift linkage, plugged with a 1/8" NPT plug. The temperature sender can screw right in there. Although putting it into the pan would let you use it as a drain plug, you'd have to weld in a bung for it...not an option for most of us shadetree mechs.

Most gauges are in the $50-$70 range. Pep Boys has the cheapest by SunPro @ $40 for a basic black 1/4-sweep face. I had bought it and a silver/white 1/4 sweep Autometer Pro Comp gauge for $55 but ended up returning the SunPro because it appeared that one's sender went in deeper into the tranny case than the Autometer's. I didn't want to risk it hitting anything inside and could find no docs as to what was the allowable depth limit, so I played it safe.