Hard going in and out of reverse

Theres only one of three things it can be. Well 4, but if the same parts are in it now as before then 4rd doesnt count. So 1) the cover is interfering; in which case pushing it up may help, but more than likely the reverse lever is wrong-part, or 2) the reverse detent tube has been driven down too far, or 3). the reverse lever is not deep enough into the cover, and the external lever is dragging on the cover.
These are basic bench checks, and the shop should have corrected these before it ever got back to you. I would take it back. However, the the last two are easily field-corrected. Unless the o-ring was torn;then its a complete tear down.
Im off to work now, so perhaps someone else will chime in. Ill check back later.