Read the tips on 'burning in' your amp with an mp3 player or similar - your amp will sound better after 20/30 hours playing time...play that mother!

I may be wrong, but isn't a decent amount of mid content essential to smooth OD? 

I get a new strat next week with similar pick ups to CS69's!! Maybe that will help me.... I have put the mp3 player on today for 8 hours, I will do it all over again tomorrow!!!

I just find at the moment my tone is flabby, its frustrating I get some good clean sounds then hit drive channel and it sounds great with very little gain, almost blues like tone....

But when I want to up the gain its all over the place.... Just a normal G chord sounds like crap no definition to it.... My amp is too dark and muddy... Do you think burn in will fix this??

try the amp in jazz mode when using the OD channel
turn up the bass and mids, treble to taste....
you will find the OD tight and punchy and singing when PAB is engaged

i find also my EV12l copes better with the huge bottom end than my G12-65........i do use both together, but thank god the EV dominates

Can you make some sound clips for us to listen to? Breaking/burning in the amp will ten to get rid of any high end brittle or harshness. While the Jazz mode is less gainy and in turn may seem like it is more clear, it's not an answer for an amp that doesn't sound good in Rock mode. You should be able to obtain great tones in any position on that amp.

Have you checked the bias and made sure all the tubes are functioning properly? Something doesn't seem right with the amp. Getting some clips for us to listen to will help hear if there's something wrong with the amp. You really shouldn't be having this much trouble with a properly working OTS. (well, assuming that the guitar is functioning properly)

does yours have the OD trim on the inside or the outside of the amp? sounds like it might be set a lil high

Gregg

hmm, you may want to try turning it down a lil and using either a clean boost or PAB for lead work. Also, make sure you have your Bass turned down a bit with the Celestions, they can get a bit fluby if ya don't.

I keep my trim at around noon, but i have found that i ride my volume and tone controls alot more with the BM to keep things balanced, i think it's the nature of the beast, especially with the G12-65's. When i had the Eminence Delta 12's in there, it was a whole other ballgame...