What engine are you running? If it's a six, you might need a reservoir tank to retain enough vacuum, especially if you're using one of the tiny boosters with a 6 or 7 inch diaphragm. The big vacuum line will help, but I'd suggest putting a piece pf PVC pipe a couple of feet long with caps glued on both ends under the cab inside a frame rail, and routing the vacuum from the engine to it through a check valve, and plumbing a line from the reservoir to the booster. You'll get 2 or maybe 3 brake applications before you run low on vacuum. Paint the pipe flat black and it will virtually disappear.
Jerry
