Slow forward motion.

yes it is normal leave it alone if it isn't broke

MOST likely cause is a worn/failed drive belt. I'd replace that first - be SURE to use a Kevlar belt or you'll be repeating the repair in a very short time frame.

Possible transmission fluid issue. Drain, Fill, Drain, Fill.
Call dealer or check online to find which fluid it takes. It's probably 20w-50.
Look at sticker underside of tranny to fetch its model number then look it up online to see parts shematic for transmission.
Parts shematic shows the amount and type of oil.
You will have to work the axels and do the transmission purge located in your manuals first few pages then top it off its last few 8 or 10 ounces.. (unboxing)

Possible carb dirty.

if you go to cub cadet.com click on info center tab then owners manual put model and serial number in it will show you a diagram

sounds like the safety switch under seat may be lose and moving while tilting

You've solved for some of the equation. Spark. Fuel. Air.....all in the proper sequence. Now, what condition are the plugs ? I'd change them out if they have any wetness to them. Check your fuses as well. Another thing is the 'safety switches' - located in seat, on parking brake, etc. One of these could have come undone or gone bad/loose wire. I'm thinking the latter....

On the transmissions, there are bypass levers...make sure they are pushed in and not pulled out

Yes, there is a switch on the motion lever on the transmission, but there is also a relay switch that is taped to the fuse under the hood of the mower...if this goes bad, the deck will not come on

How do you disconnect the reverse safety switch on a cub cadet 2160... where is it located?

Cub Cadet Z Force 44 seems to be going quite a bit slower than when I first bought it. Drive belt seems to be fine.