I am replying to give you some food for thought. I now have Tembrens on my 2008 Dodge 2500 CTD. I installed them about 2 years ago after we first bought our new fifth wheel.
When I first installed them the clearance from the axle was about 3/4 of an inch. They have worked well and I was well pleased until now. In summary, the timbrens are now only about 1/4 inch away or so from the axle. I can only guess from having my heavy superglide hitch in it year round and towing with about 2,700 lbs extra on the rear axle for about 30 days a year. The truck has about 103,000 miles on it now so a little suspension sag is to be expected.
Since the gap between the Tembrens and the axle is now about a quarter inch, the truck does not ride well empty at this time. It does not take much of a bump and the truck hits the Tembrens harshly. It still rides well when I am towing and supports the pin weight well. I think the harsh ride comes from being on the stock leaf springs and then hitting the Tembrens when we hit even small bumps. Until your suspension sags a bit, you will not have this problem. I might not have this problem in another 50K miles because the suspension will have sagged enough that I will be well on the Tembrens at all times. But for now, the truck is riding terrible.
I have ordered and will be installing a set of Firestone ride rite air bags next week. I liked not having to sorry about air pressure with the Tembrens, but the suspension sag leaves me much more willing to trade off air pressure concerns for a decent ride when empty. Hope this helps.