I've got the GroundForce 2/3 drop on my 4th gen Crew cab sport, and although I love the look I've found that the Rear sits about 1" lower than the front.
And the ride is harsh to say the least, thought I'd wait a little to let it settle in before checking it again.
Checked it out and found that the Rear end is sitting on the bump stops supplied by G/F...
Spoke to ground force and sent them some info there now checking to see if I've got the correct rear springs.
I'll let you know our things work out.