it's normal for the rear axle to move foreward and backward during suspension travel. that's why your driveline has a slip yolk at the front. the longer the link bars are the less foreward and backward motion you have thru the same suspension travel.
i've never actually looked at or thought about one with a 2 piece driveline. mine's got a 2 piece... hmm. maybe you can go to a one piece and just be sure the driveline won't hit the back of your cab.