I’ve read the other posts in regards to this issue.
Here is my communication with Firestone

 

Maybe I was haphazard in my measuring, but my 2020 Platinum FX4 F350 was only around 40mm, and the 2712 did work on my truck. Or well....I installed it last week with no apparent issues anyway, haven't towed with it yet as my new trailer is in production.

The 2712 is the 7500 pound bag though, but I can't see why the 5k bags would be much/any different. Your 55mm height could be an issue I suppose as I'm not sure if I would pick the lower hold or the middle. I would think the middle would work, and just compress the bag a little more at rest. If you run 5 pounds in them and use the middle hole, you might see slightly elevated rear ride height, I am running mine empty for that reason.

 

Mine was also 40 mm, I put the same kit in mine, it is a 2020 F350 SRW 6.7L with FX4. They went in fine, I run 5 lbs in them, I do think the ride height is probably up just a bit, maybe 1/2"?

I don't believe FX4 would have any impact on the measured height, the FX4 is only a few features and skid plates, I don't believe in 2020 the shocks are different anymore. I did put Bilstein 5100's in shortly after purchase.

They have worked fantastic towing with an 800lb tongue weight.

 

The FX4 package shouldn’t matter if it works on a non FX4 it will work on a FX4

 

How heavy are you towing? My father just bought a big toy hauler, 17,600 lbs GVWR, and we put stableloads on his truck. I have the 5000 lbs airbags on my truck, both trucks are identical, F-250's non High Capacity. I hate towing that trailer with just the airbags. The stableloads engage the overloads at ride height, so when you start lowering the trailer on to the hitch, it's already sitting on the overload spring. The airbags are squishy and bouncing and never allow the overloads to engage. I am going to get rid of my airbags and get the stableloads or a DIY version. Seriously look at this option if towing heavy.

Edit to add: Basically stating that the overload springs provide way more stability than the airbags do. Either sag and let your truck ride on the overload springs or buy the stableloads.

 

I recently installed the 2620's (the 5k springs) on my 20 250 FX4. I had no issues, measured at 40mm. I did replace the long carriage bolts they include with 5 1/2", 3/8 bolts instead, was just enough to get the nylocks fully seated.

 

Regarding stability, if you plumb the airbags with a common fill connection, without a shutoff valve between them, the airbags will transfer air from one to the other when you are cornering, thereby making the truck feel more tippy and less balanced. With separate fills or better common fill with a shut off valve in one side, so that once filled you can close it and isolate the two sides, the airsprings when inflated will provide more roll stiffness.

 

My airbags are separate air fills. Also, my bags were aired up to 60 psi in my scenario above.

 

So you’re truck measures 40mm or did you install the bags at the 40mm setting?

Does your truck have the overload springs (camper pkg)?

Mine does not have overloads.

 

I've never experienced that in air bags.

Semi-trucks have a common fill for tractor and trailer as well.

 

My truck measured 40, but it is an F350, so full spring pack.

 

Mine measured 40mm. I also do not have the factory overloads.

 

I ordered a set of the 2620's for my truck.. (which was only built yesterday so I don't even have the truck yet) I talked to a guy at s.d. truck springs, he assured me firestone has it figured out and this one will work with the fx4 package...Unkown to me, my kids also bought me the same ones, lol. I do not feel like paying for shipping for the 34 pounds back to s.d.. So either I'll have spares of everything or I'm going to sell the extras. Kevin

 

I bought the 2620 bags for my 2020 F-350 SRW CCLB FX4 but the bracket wouldn’t seat properly on the axle because of the hard brake lines being in the way. Firestone said I needed to bend the lines. Has anyone else had to do that as part of your installation?

 

I never experienced this either and I always have a load. I put bags on everything love them.