I get about 10.6 mpg out of my 3.5 on Grizzlies. Same driving on normal road tyres gets about 12.5 mpg.
A run along quietish country roads nets about 14mpg on the Grizzlies.
I have the vicous coupling Borg Warner box. Don't know if that makes a difference
Air ratchet is good. Nail gun excellent! The windy gun seems a bit tempremental, but bucked up once a bit of oil was added so probably needs to bed in a bit. Makes life a lot easier wheel changing. Both the windy gun and the ratchet come with a set of impact sockets too.
Don't know if they would handle every day professional use, but they are a welcome addition to my workshop cabinet.
Roverdrive