Just bought a new Trek 8.5 DS hybrid with SLX rear derailleur and Deore shifters. Been riding a 1995 Trek 7900 with Deore XT derailleur and grip shifters.

Took the 8.5 out on its first ride today and trying to get used to the shifters. Grip shifting is easy---snap up or down, a gear at a time. With my new bike, kind of depends if you fully depress or lightly depress either shifter. Also, seems like it wants to shift two gears at a time in the smaller gears. Finding myself having to shift twice to get the gear I want.

What gives? Not adjusted right? Maybe it's just that I need to get used to shifting better?

I think you need to learn how to shift/move the shift levers better then you do now. getting the feel of how far to move which lever to make how much of a shifting possibility is, like other aspects of coordinated movement, a learned practice.

Kind of like when Grip Shift first came out and riders tried it without previous experience. Many complained about shifting imprecision, massive wrist movements that interfered with their grip and the inadvertent shifting when "working" the grips strongly.

You got past these issues with Grip Shift, now you need to get past the lever shifting differences. Andy.

+1, get some lessons on how derailleurs work ... you need to think some..

read the terrain changes, and anticipate the gear ratios you need for that slope.

brifters do indeed require some "technique". twist grips are, in a sense, easier. Brifters -can- shift more than one gear if you push a lever in all the way and hold it a bit. When your brifter is calibrated properly it should indeed take a single click and it should shift well, but you can push it past that single click and you can also fail to push it hard enough to click it all the way. It may take a few miles but after a while it will seem like second nature.

Since it's a new bike, take it back to the LBS to address your concerns.
It might simply be a matter of the barrel adjuster needing a 1/2 turn.

Brought it back to LBS and there is a problem. Tech spent lots of time with adjustment and it is much better.....but not perfect. I'm going to ride it for awhile and see if it can be adjusted further in a few weeks.