Okay, I know it is a bit late for you Jim but I found your request while searching for the answer to you question myself. Apparently there is not solid info on how to do this for this model of ProForm. But I do know how to do it as I did it without any helpful instructions. So, for anyone else that may need this info, here it is.
You can order a new walking belt for thew ProForm Crosswalk GT for about $80. The instructions that come with this order will not be exact to your model and can be a bit confusing as nothing seems to match the GT. First you will need the following -- small flat blade screw drive, 3/16" hex wrench, 7/16" wrench or socket set, a medium sized philip head screw drive and a large head Philip (you might get the med. sz philip to work but a couple of screws I had to remove were really tight and need the larger driver)
Setp 1, using the small flat head screw drive slide it under the plastic side step rails. They are stapled down to the deck. The staples will be in pairs, one on toward the belt and the other toward the outside of the step rail. Gently lift the step rail,until each staple is comes free or the plastic step rail pulls from the staple. Don't worry you can remove the staples left in the deck later and then when you replace the step rails use small screws. These side step rails are really flimsy and do nothing but cover the outer edges of the deck.
STEP 2 With the side step rails off you will see 6, three on each side, large philip head screws, remove these. This will enable you to lift the deck and slice the belt off, but not just yet.
STEP 3 Remove the front shroud, that is the covering on the front lower area ahead of the walking belt. The motor and drive belt and electronics are inside this cover. There will be two philip head screws on the lower part of each side and two in the front. Remove these four screws and the shroud will lift off.
STEP 4 Facing forward, like when you are using the walker, you will see a bolt on the right side of the front roller. Take a felt tip marker and mark the threads toward the front the the roller, maybe put a mark on the top of the bolt head too. Using the 7/16" wrench or socket remove this bolt. The roller will fall loose.
STEP 5 Go to the back of the treadmill to the smaller shroud covering the back roller. Facing toward the front of the treadmill, you will see two HEX head screws, left and right, you will use the 3/16" hex wrench to remove the right side only. The rear roller will fall loose, still connected to the left side.
STEP 6 A helping hand from a friend would help but I did this by myself so it can be done, but if you have a friend, hey, put them to work. Pull the old walking belt free. To do this you will have to lift the deck up at an angle high side to the right. The rollers will pretty much stay where they are as you pull and tug the old belt from under and around the deck.
Step 7 The new belt goes on in reverse.
That's it. Put everything back. Adjusting the belt is not that big a deal either. Before putting the plastic step rails back on start it up, low speed only, watch the belt and see which way it moves. Remember the ink mark you left on the threads of the front roller bolt? That will put you right back where it was originally so from there you only need to watch the back of the belt and use the HEX screws, in or out, to control the flow of the belt. small adjustments, it does not take much to make the belt crawl from one side to the other. The tension of the belt will be greater in the middle of the walking belt, the part touching the deck. The out side edges of the belt will curl up a bit and when you lift with your fingers 2"- 3" is okay but the middle will be lower and should be lower. That should do it. I hope this will help the next person wanting to keep their treadmill. It is not very often a piece of equipment is worth retreading but my machine runs just like the day I bought it and the only thing to wear out was the walking belt.
Peace in the loving Name of our Savior, YaHshua
Dan
March 2009