Golden Pass reservation Zweisimmen to Lucerne

I don't think you even need to reserve seats on these segments, nobody else does.
Ah, you are already annoyed at Rail Europe. You're learning. Once you've kissed them good bye, you will have achieved enlightenment.

You may be missing the fact that reservations are not required. When that's the case, I would not bother to reserve. Rail Europe more usually charges $11-14 to book optional reservations, but I see that this rate is $18 and sure, that's another reason to skip it.

So on June 2 we should be OK to get on the panoramic car of the Golden Pass without reservations all the way from Montreux to Lucerne?

[Edited] Reservations for the Panorama cars on the Montreux-Zweisimmen leg are optional for individuals, but recommended if you want to be sure of a seat. (Reservations are required for groups of 10+ and the train is popular with groups.) The remainder of the route has more frequent service and really doesn't need reservation. This timetable PDF may be helpful (note the key in English).

Mark, this is marketed as the "Golden Pass Express", it is in fact three (sometimes four) different trains end-to-end run by three different railway companies:
Train 1: Montreux to Zweisimmen
Train 2: Zweisimmen to Spiez
Train 3: Spiez to Interlaken Ost (sometimes trains 3 and 4 are combined)
Train 4: Interlaken Ost to Luzern

The panoramic cars are, AFAIK, only on train 1. So this is the only one you need to reserve.

BTW, the company running train 1 has just ordered some special trains with adjustable length axles so they can run one train through from Montreux to Interlaken. This is not due to be operational until December 2020. See here: http://www.railwaygazette.com/news/traction-rolling-stock/single-view/view/mob-orders-dual-gauge-golden-pass-fleet.html

The train between Interlaken Ost and Luzern is a narrow (meter) gauge and all of the cars are panorama. It is operated by Zentralbahn and runs every hour under the name Luzern-Interlaken Express.
https://www.zentralbahn.ch/en/interlaken-express

Thank you everyone! I have been studying this route and I am pretty familiar with the train schedules and I know that right now reservations are not possible for June 2 on the Montreux - Zweisimmen leg due to construction that is scheduled to end on June 1. I know that reservations are not required on the other segments but I guess my main question is should I desire to make reservations on segment 2 and 3 am I better off just going to https://tickets.goldenpass.ch/reservation than I am going thru Rail Europe?

Also, when I look right now on that site I see that in carriage 1 (which seems to be the only 1st class carriage) there is only 1 seat left on the 13:04 from Interlaken OST to Lucerne. That makes me nervous that 5 1/2 weeks from now that entire train could be reserved. Am I missing something on this part?

Thanks again!

Solution is to reserve the 14:04. 10 spots open. That way, you can take a break for an hour at Interlaken Ost station. Snacks and beverages will be cheaper than on the train, and more variety. Take a walk around the back of the station where the lake boats dock and, if nice weather, some outdoor cafes.

should I desire to make reservations on segment 2 and 3 am I better off just going to https://tickets.goldenpass.ch/reservation than I am going thru Rail Europe?

Always go direct to the company running the trains if possible.

Also, when I look right now on that site I see that in carriage 1 (which seems to be the only 1st class carriage) there is only 1 seat left on the 13:04 from Interlaken OST to Lucerne. That makes me nervous that 5 1/2 weeks from now that entire train could be reserved. Am I missing something on this part?

These trains are not just for tourists, locals and everybody else uses them to get from A to B, shopping, going to work, visiting etc. And nobody but tourists plans such trips 5½ weeks in advance, more like decide on the day. It is only the extra tourist panorama wagons that are reservable. Everybody else will just buy a ticket on the day (or use a pass) and get on the train.

I was able, last week, to make reservations for a June 24 Zweisimmen to Montreux leg on the train. I went directly to the Golden Pass website: www.goldenpass.ch/en