Make sure the antenna wire is fully extended - run all of it thru the antenna tube and then secure the part outside the tube with something like fuel tubing or heat shrink. I've seen some that keep the excess inside the RC, bundled up next to the tube, thats not what you want to do for range.

If there's a longer antenna tube available, use it, I use 14 - 16" tubes which help range. Make sure both crystals are fully seated. Always run with tx antenna fully extended.

You will not get the range out of AM you'd have with FM. If these tips don't help, upgrade to FM of a good 2.4ghz system.