I believe there are spacers you can put in to make up for the difference in spring height. You'll also want to see if you new spring are wider than stock. There was a member on here with taller/wider springs (MiRamDriver, he has a towing thread with then in this section. 10,000 lb trailer post) and his airlift bags didn't work because they couldn't expand wide enough to fill in the Springs.
I've got stock coils with a rear 1.5" coil spacer for my lift. Here is a before and after pic with a 900 lb pin weight on my truck. There is no weight distribution hitch on in the pic, the truck is taking all the weight. They made a nice difference!
Now the third pic is with my dump trailer on back. I believe the pin weight is around 400 lbs. It leveled right out at 30 lbs in the bags (35 is max). Leveling out is not the only think these airbags will do for you! The truck will handle better with them on. You won't get as much trailer sway or that "sucking in" feeling when you pass a transport. I didn't even know the 4000 lb dump was on back. It was amazing!
They say that the bags will level out 1000 lbs. That's not exactly true. As you can see the 900 lb pin still squats. That's a lifted truck thing, on a stock truck with a 2" rake it would look more level. What I did find worked well was when I put weight in the box. I had my 600 lb atv in the box with only 12 psi and the truck was completely level. Same deal with my sled (see 4th pic) This is because the weight is right over the Springs instead of on the hitch further back.
For the money you can't go wrong! Definitely couldn't pull the travel trailer without them! The steering was way to light, could have caused an accident. The airbags fixed that by eliminating a lot of the squat! Plus it looks way better lol.
