[suicideneil]

Hmmmmm...

In all honesty (I have been looking at lots of these things lately), I think your best bet would be one of the Garmin handheld units, like the 'Etrek' or something similar used by cyclists or walkers.

Only other real option is an rpm sensor like the venoms have, but it comes as an optional exta with the Eagletree data logger. Trouble with those is they measure motor rpms, so any kind of wheel spin or slippage can result in a very iffy reading. I would suggest the handheld garmins- small and light eough to mount in the truck without musch hassle, and some models can be linked to a PC to download/upload data too.