Think about it this way:
You put the car in D and it shifts a hell of a lot more than you put it in R. Logically, R gets a lot less wear and those clutch packs will last 10x longer. However, it's always shifting/downshifting 1-3/OD, so those clutch packs bet a lot of wear. So yes, it's definitely a symptom that your problem lies in 1 of 2 areas: sticking/worn out Valve Body bore OR worn out clutches. Regardless, with that many miles, a rebuild is due.
