You have my sympathy. I agree, in today's GB environment a Guam is pretty useless. I'd use the Pensa instead and AA my way up to at least BB3.

most bb1s (at level that is) will have hard time at gb today...

options are

1) going back to CA (PCA preferably and AA until bb2/3... except for the UK ^_^ don't know its PCA settings)

2) getting a PBB if you can afford or an ebb if you have won last event (preferably pbb :) )

3) like me i just grind my bb1 and suffer hellish torment of grinding out from it :D (it would be helpful if skirmish rooms are available but i can only see 1 succeed in starting and after that  less players joins at it)

As noted, the game is currently geared toward torturing poor players in BB1s. The game modes that old dogs like myself used just don't exist as viable options anymore. If you can afford to fork over some cash, getting a Sevastopol is highly recommended. It's an amazing ship that's usable at level and a powerhouse at level 80.

Otherwise, if you've done other grinds and can afford to do so, I might also recommend leveling up your engineers and gunners to 80+ and then go back to the Guam. Once you have high speed, a decent overheat time, and a tighter spread (and 900 sd), it's actually a decent ship in GB. 

The truth is that, unlike some other nations, none of the US BB1 and BB2 vessels are that good without a high level crew. But they can be deadly with that high level crew.

or make another BO that will choose the Nevada line... 

Best thing to do is buy the mighty Pensacola (PCA) and go for an AA its awesome plus great XP :))

play asw (possibly with a sonar escort)

start the battle with spotting out subs, once you kill them you can get to the line to help out against rushers.

killing subs will raise your winrate since they have more effect on the battle outcome than AA-ing has nowadays. it also gives you some better insight in what to do & not to when facing subs in larger BB's.

the last bb lines i started from scratch went trough the lower tiers pretty fast, playing this way for the team. 

if you have lvl'd 2 BOs for US and dont want to spend money on premium stuff, i recommend you to switch to the second line with the nevada as BB1. its a tiny and sneaky BB1 and you wont draw that much attention (its a bit slow but you will learn to cope with that ;) )

once you got your gunners and engis to a reasonable lvl (70-75) switch back to guam and play careful hit and run (you shold be kinda fast now with it).

oh and a tipp more related to BB gameplay:

NEVER skip playing a BB1 cos its hard and you got low range and stuff like that! if you master playing a BB1, aka doing 10-20k dmg avarage per battle and surviving more often than diing, you will have a fucking easy time with later BBs and your enemies that mostly skipped the BB1 for their PBB ;)

Try to play Skirmish.