I bought a used L-2500 about a week ago. I do not know the guage of the strings that were on it but I put a set of 40-60-80-100-130 guage. I have not been able to set it up to G & L specs or to the action I prefer. According to G & L, I should have between .018 and .022 relief in the neck at the 8th fret. I have turned the truss rod ALOT! I would say I am up to 23-1/8th turns since I got the insturment 8 days ago. I make an adjustment the neck moves, I tune to pitch and everything is cool for a few hours. Then the neck shifts back to relief greater than 30. I am afraid of turning the truss rod much more. This is moving my action from just a hair below 3/32" to just a hair below 1/8". I can not get the action any lower or I buzz out at the 15th, 16th and 17th. There is a shim in the neck. Has anyone experienced this? Do you have any suggestions? Do you know a good luthier in the Chicago area?