Don't know what year truck we're talking about here but you won't be able to get a 3 to 4" drop out of mono leafs. You can get an easy 2", maybe a little more with monos. Dropped axles are the way to go if you want to go lower and still have good spring travel. I've got a 3" axle and also removed 3 leafs from the front of my '53 for a 5" drop. You can check prices and get info from Sid at droppedaxles.com.