The 4-speed has a weak OD and will need attention.
Frames are junk, including my current 06
JBL can be tough to integrate aftermarket head unites
I whole heatedly disagree with the above listed points:
I have towed all kinds of trailers in mountains, desert heat, Florida humidity, going slow, crawling in traffic, hauling ***, up to the Max GVW and never had a tranny problem. All I have done is change the fluid every 20,000ish miles. It's no different than any other truck, don't push it to the limits every day and you'll be fine. I have had quite a few friends who have and 1st gens and none of them have had a problem. One buddy has the TRD supercharger on his and beat the ever loving snot out of it for years, never flinched. People have to remember, it's not a heavy duty truck, its a 1/2 ton designed to be comfortable and easy to drive, not tow a house through the Rockey's.
The only problem with the frame is they rust out when they have been up north for years, and Toyota has done a good job of replacing them ( mine is 100% rust free, despite countless trips driving down Daytona beach).
The JBL is junk to begin with. Just add a aftermarket head unit and bypass the factory amp, it will sound much better and be louder. I went a little further and went with a Pioneer head unit, Kicker separates in the front and read doors, and two JBL 8's in a Q logic box under the seat. The amp is under the drivers seat. It's is loud, has plenty of bass, and is not noticeable if you look in the windows.