Dura Ace, Thumb Shifter shifting problems

I have a Trek 1500 with a complete 7400 Dura Ace group except for thumb shifters. The thumb shifters are Shimano Light Action. The rear shifts just fine, but the front is having problems. The LBS can't figure it out either. In the stand, the front shifts smoothly and easily. In the real world with someone riding, the chain does not want to go into the big ring. The thumb shifter become stiff and it is much harder to work the lever to get the derailleur to move. The shift is very clunky and it will not complete the shift every time. The pressure needed to move the lever is bad enough that it hurts the thumb. This is an upright bike for my wife and she will not be able to shift with that much pressure. Why would it shift easily to the big ring in a stand, but not when on the road? We swapped the cable for new one even though we had just installed a new cable. I'll post pictures if that helps.