My bathroom shower takes forever to get even lukewarm but the bathroom sink gets plenty hot. What could be the problem?

For scald guard faucets -You may need an adjustment on the temperature setting on your shower faucet if it is a single lever handle faucet. You also may have a problem with the balancing spool in the faucet or debris in the line. If you have a 2 or 3 lever faucet the tempering valve may need adjustment. Take off the shower head and check the flow with faucet on fully hot and fully cold. If the flow is equal and adequate, you probably need to adjust the cog usually under the handle for the temperature stting. Good luck. If all else fails, call a plumber.