See ifyou can lie under the dash & get your hand on the shift cable [ or you might be able to see it ]. Get a helper to push the push buttons & you should feel the cable move with each shift increment. No movement might indicate a push button fault, but it could also be inside the trans.
Thank you so kindly for the suggestion! I will have my dad give that a go this evening when he's with the car and will get back to you. I really appreciate the time and help. More to come!