Darcane - your truck is 2wd right? Have you noticed any mileage improvements from your grill block/underpan?
I'm debating what steps to take on my Silverado. Just for fun I taped a big piece of cardboard over the grill and drove a route that I drive fairly often. I wasn't expecting much but got surprisingly better mileage.
I've driven this route 3 times in the last 2 days in similar conditions (11mph wind, ~32 degrees). The two trips without the grill block I got 17 mpg on the trip out and 19 on the trip back. After taping the cardboard on, I got 18 on the trip out and 20 on the way back!!
I'm going to have to do some true testing now to see if it is really having that much effect. Engine temp was unchanged - but the transmission temp jumped from around 130 to 175.
