With engine idling, go check oil level. Always remove and wipe stick before dipping back in for a check. Stick is in a deep tube so first pull always seems to show high oil.
Oil is checked idling in neutral. Many check with engine off, it will read high then.
Next will be to check that selector valve is moving on top of gear.
With engine idling, shift fnr and listen for any sound changes around the gear. Whine change, thunks or clunks.
Any pressure gauge on unit?