Originally Posted by jsloan

But, there are a couple of problems. The first is that if R isn't available on the BKK-NRT flight you want, you're going to have to upfare the entire return to A/E. While this will let you use your GPU, it's going to be really expensive. The second is that you do need a PE cabin on the overwater flight; you cannot use this fare on a flight that doesn't have that cabin, even though you're planning to upgrade. The only way to get on a flight that doesn't have PE is to re-fare, either to business directly or down to a W fare.

To get an idea of the fare difference, try pricing out similar flights, using multi-city search, starting from DTW. You're right that you don't want to just do a one-way search.

If you care to post your original travel dates (outbound and return), your original ticketing date (from your receipt), and your proposed return date, somebody can provide additional information -- but, ultimately, it sounds like you have enough to call UA and at least to get a quote.