I use nothing but Dexron/Mercon III in my GTP as well as the GF's GTP.
Over kill, but I change it yearly with a fluid and filter/pan gasket. Cheaper than a transmission. I prefer a pan drop method as well.
I have a higher stall converter, (ZZP's 2750 stall 245mm) and 3:69 gears, and have always ran an external cooler (B&M <24,000GVW Tranny Cooler) ever since I have owned my car. The gearing I noticed made the transmission hotter than the converter, as they were installed at separate times.
The transmission was a Big Jeff built INTENSE one with stock gears and a slightly higher stall converter when I bought it in 2001 or 2002, cant remember. Its still running its GenI diff. from them to.
~F~
