extra gauges... which one??

[Juice]

If I was to add an additional gauge to my rig, what should it be? Oil Pressure? Temp? Tack? Volt? I'm going to be doing some boat hauling this summer and just wanted to know what you all thought...

[bignblue]

Definitely transmission temp...if you're hauling with an automatic, you need to keep a sharp eye on temps! Also maybe some kinda line pressure gauge for the tranny if you can rig one up. I've heard of people installing vacuum gauges (to help ID best economy ranges) but they've all been in the engine compartment.