Originally Posted by
Al1943
Assuming that the high limit screw is adjusted correctly, I would try shooting the shifters full of WD40.
Of course you could try backing out the high limit screw slightly and increasing the cable tension a bit.
If the shift cables and cable housings are old they probably need replacing.
There is a lot of mechanical help available at
www.parktool.com.
Do not use WD40 on your shifters. "WD" stands for "Water Displacement" which is what it is really good at. Spray WD40 down seat tubes after rainy rides, and use it to clean out Chris King hubs, but never spray it into any moving parts you want lubed. When it evaporates it leaves a gummy residue of mostly mineral oil which is not very good at lubricating metal parts but is super good at catching dust.
When cleaning/lubing something as intricate as STI levers, use a high quality spray lube from a bike shop.
All of that having been said, none of this points to the shifter being sticky.