May want to go here and get this:

all about the 545RFE

 

Interesting read. Thanks

 

After reading page 21-444, I thought there might be a way to trick the tranny into staying in 3rd by placing a resistor inline with the temp sensor tricking the computer into thinking the fluid temp is less than 40 degrees. It says it delays shifting into 4th and 5th gears until it warms up. After further consideration, I recinded my thought process. Locking into 3rd gear would be great for towing those heavy loads up and down hills but without further info on the tranny, I don't know how it would affect the transmission.