Tend to agree with Gavin,
Get your track right, or as right as you can. That will cure most things
Also, with the whole Thomas series there are rules that I have found I need to observe to ensure that things run as well as they can.
Avoid LGB R1 reverse curves, as the long rigid wheelbases, and even the wagons really object to these.
Fit swivel couplings on the longer stock, or you will relegated to LGB R2 or larger.
A little extra weight in the locos helps too
The Bachmann Couplings are fairly awful, especially the large D type ones, and none are that positive, or easy to couple, so I replaced all mine with proper LGB ones that work well, although I use swivelling Playmobil ones on the coaches and the brake van.
Finally the wheels on the locos are prone to wear, so after several years those on my early 2010 vintage Thomas and Percy were replaced with new factory parts obtained from Bachmann. The wheels are fairly cheap, but postage and customs duty take their toll (Sorry). Another issue is that Bachmann don't actually offer a spares service, but sell off left over parts that they might happen to have, or more often - might not! So if you want driving wheels for Emily, James or Toby, forget it!
Perhaps Dan is right - go battery!
James