Amy - A couple of things:
1) Those tires don't look like they are on 13" wheels. TM used 14" wheels in 2004, so that would be consistent with what one would expect. Once you can get a better view of the tire, you'll also want to look for the 4-number date code, normally enclosed in a circle, which tells you the date of manufacture. The first 2 numbers tell you the week of the year, and the last 2 numbers tell you the year. A code of 0406 means the tire was manufactured during the 4th week of 2006. If your tires are less than 3 years old, you are probably fine. If they are 3.5-4 years or older, replace the tires, regardless of how the tread looks. Otherwise, you are risking a blowout, which aren't pretty (or safe). Whenever you replace them, consider replacing your wheels with 15" wheels to even further reduce your chance of blowouts. Lots of info on that here on the forum.
2) A 13% grade is pretty steep. That's about 7.5 degrees. My driveway is 6 degrees (about 10.5%), as you can see in the picture in post #24 of this thread, and I can get up the driveway just fine with the 2" lift kit (using 14" tires, too).
http://www.trailmanorowners.com/foru...t=10910&page=3
When the TM is connected to my TV, it is parallel to the ground.
3) I too would bet that placing some 2x6 or 2x8 or whatever boards across that dip, and then backing over the boards, should solve your problem. But as others have suggested, I would get the lift kit as you'll encounter other spots like this during travel. When you do this, you also may need to raise the ball on your TV.
Dave