For about one year i've been playing the extreme of bass trombones, and seldom i've got the chance to break even the C above tuning Bb because the repertoire just don't ask for it. For example, previously a while ago my school band was playing "Hymn for the lost and the living" some 911 commemoration piece that asked for tons of Double Low Ds and Bbs. Back in tenor now i'm suffering from the low-notes overuse syndrome, and i can't to pitch double high Bb properly. Fortunately i can play High F and Gs without problem, but i would really like to regain my previous high range. Any suggestions?

i'd say long tones wouldn't hurt all too much. and i would say to play in the upper octives to get your muscle memory back in your chops. maybe thats what your problem of hitting those notes are...but then again i could be very wrong, but thats what i would say

G'day
Start doing lips slurs and long tones and keep persevering with the problem. It will eventually regain. From playing all of those low notes you have simply forgotten how to play in the upper register. And you have created a bass trombone embechure. Just do the lip slurs and practice and it will come.

i'm not gonna give range extension exercises because i'm sure you're gonna get a ton anyway. besides, if you're maxing out around a high G or so, i'd say there is probably some other fundemental problem going on that needs to be adressed.
but i do think you relay an important message to all players. BALANCE. we need to work all ranges of our horn, all dynamics, genres. played a lot of low notes? play high. played a lot of of lip slurs? work some long tones. you get the idea. in my job right now, i don't even use a large tenor... and won't for some time. but i guarantee you , i work on a large tenor every day. i do a lot of lead work right now, but on my own time, i still work my low range. it's all about balance, being thorough, and preparing yourself to play whatever may be asked of you. good luck.