If you are keeping it 100% stock, and can resist the temptation to beat on it more than once a week, the trans shouldnt be an issue. Just put a cooler on it and be done. If you plan to do just some small mods like a CAI, mailorder tune, catback, I would do corvette servos and the cooler. Anything beyond that, you REALLY need a transmission done. My stock transmission never gave me any trouble, but I never drove the damn thing either. There are numerous stories of guys with stock trucks destroying the trans before even hitting 50k miles.
RPM and Finishline are equal in my opinion. Both are very quality built units and will hold up to everything short of an all out race truck. Depending what you want to do with the truck will change what stall you want to put in it. If it will be used for towing, stick with a Yank PTB series converter. The lower the stall, the better the gas mileage, and the more driveability it will have. My truck has a fairly loose 3600 and it is difficult to accelerate from a stop without getting pretty high up in the RPMs. Inclamate weather is also something to consider with a large stall as well. The truck will be in higher RPMs, and powerband, which will break traction pretty easily in snow.
A