Are you positive the manual says GL-3? My manual for my 05 says GL-5 for the differentials and GL-4 or GL-5 for the transfer case. GL-5 is really, really common for differentials no matter who the manufacturer is. Just make sure the bottle says it's OK for limited-slip differentials if your truck has a mechanical limited-slip rear end. The 05 to 08 Tacomas with mechanical limited-slip differentials have an "LSD" decal on the rear differential.
I believe there is no brass or bronze in differentials or transfer-cases, just manual transmission synchros (someone correct me if I'm wrong). I found some info on bobistheoilguy.com that indicates modern GL-5 can be used even in components with soft metals. Just get a reputable brand and you should be fine. I like Amsoil A LOT! Anyway, here is the info I found and I hope it helps:
"GL-5; Specified for hypoid gear service but with shock loads and severe service operation. Usually meets Mil-L-2105D and in most cases, is the multipurpose automotive gear oil. Most 75W90 to 75W140 grades meet the GL-5 classification. This grade has a high level of Extreme-Pressure additives that could be mildly corrosive to nonferrous parts, such as brass, bronze and aluminum parts. Most of the modern GL-5 lubes contain metal deactivators that prevents attacks by the extreme-pressure additives. In addition to EP additives, these lubes contain rust inhibitors, defoamants, friction modifiers, thickeners, and Viscosity Index Improvers."