Battery life suggestions?

I had a first-gen iPhone (several, actually), jailbroken and unlocked, running on TMobile in the US, for years. No problems, perfectly acceptable battery life of 1-2 days per charge. I recently got a 3GS (old bootrom, BB 05.11.07). It worked fine when I first JBed and ULed it on 3-point-whatever, but somewhere along the line to 4.2.1, something has screwed up the battery life. I'm lucky to get 4-5 hours out of a charge if I use the thing at all, and it will drain totally flat if I fail to charge it overnight.

I've not installed anything from Cydia beyond ultrasn0w and SAM. I just did the SAM install this week. It installed successfully, but if anything it has made the battery problem worse. I'm a pretty basic user, but I'm clever enough to read and follow instructions, and will look for solutions on my own before asking for help in a forum. I'm stumped, though, so: any suggestions?

So (days later):

I redid the SAM thing a couple of times, very carefully, and it never helped. So I started from scratch, made sure my phone was deactivated, removed SAM from my phone, and activated it with a valid ATT SIM. I changed back to my TMobile SIM and all was well--except the battery still drains every bit as quickly as before. I'm now NOT hacktivated, as far as I can tell. What else might be draining my battery so quickly?