I did some checking for you and the stock slave cylinder for your truck is a 13/16". I'm not sure that going to a 1-1/4" slave cylinder is going to work. I'm afraid the volume would be too large for a any master cylinder less than 1". A 5/8" master cylinder would not push that slave cylinder far enough to disengage the clutch. On the other hand, a slave cylinder on the order of 7/8" or possibly 1" might work.