Here's a little excerpt from one of my posts....easy enough to cross reference the part # of a stock unit at the dealer to see if your model year matches the parameters of the ones I've listed here. If these Ranchos fit your year in stock mode, then it's a simple matter to consult Rancho etc. to get the next longer size etc.....
I just acquired a 2007 fg140. I found a thread on this site where a fellow had installed Rancho 9000's on his 2003....so I know they fit 03-07. I installed them in conjunction with the Timbren bump stops on the front and was very pleased with the results. The jolts from expansion joints/sudden dips etc. are greatly reduced. I ran them initially on the lowest setting which did not provide enough rebound damping. Then I cranked them to midpoint and the ride was nearly as severe as w/ the stock parts. (This was unladen at 8600lbs)....I finally settled on setting #2 (of 9) on front and rear. Obviously, there's plenty of room left for adjustment. The part #s are: 999117 (fr) and 999113 (rear). The Timbrens increase the distance substantially between the stop and frame. You can score the shocks on Amazon for $89-$110 each. Timbrens run about $200 on the net. The Timbren rear set is $400 and I'm tempted to try that but have not found an opinion from someone who's tried them. Try sticking your hand between your bump stop and frame...bet it won't fit in there with the stock stops....that's what you're hitting. Then your worn shocks are letting the springs catapult you into the air... I believe the perfect FG shock would have adjustable compression and rebound damping. Every situation is different. I run Bilsteins on my 5.7 Tundra and have run Bilsteins, KYBs and Rancho 5000's in the past on Dodge diesels...The Bilsteins always seemed a bit too stiff on compression while the Rancho's were very progressive and comfortable. (Body roll was fine as I install sway bars on everything I own. I'm exploring that now for the FG. I think a sway bar would benefit a heavily laden camper FG too. I really think Rancho's really got their valving down and I'm pretty sure I'm going to fit their stuff to anything I get in the future.
