Castorian Enknuckes-A (aka TT-Fist) not gaining levels

[SnowLeopard]

I bought a few TT fists and have been tiering them up for fun. Got two to 0.9 and started on a couple others when I had accumulated what I needed to upgrade one to 1.0.
So far so good. Started using the 1.0 and got it to 1.1 and now it seems stuck there. I've gone through almost 2 full repair cycles.
I decided to upgrade another one, but the one with the best numbers was only at 0.3 so went out to get it up to 0.9. Almost a full repair cycle and it's stuck at 0.3 still.
In both cases the numbers are over 100, and other gear I've used has gained tiers (both L and non-L), but I haven't used any other non-L weapons.

Has anyone else had a problem gaining tiers on TT-fist?

 

[Immortal]

There are numerous threads and posts that document higher tier items are more difficult to increase in tier rating. Search Marco's Posts I seem to remember him making a reference to it being intentional.

On topic, I have also foundthat if you have it easier than normal tiering to 1.0

Personally, I tiered a cust MF-213(L) to 1.0 in 70 probes, and I think it took another 70 to get to 1.1