Ken - you were right. I got two responses yesterday afternoon. For the benefit of anyone else reading this thread, the problem is indeed voltage loss, not signal loss over the long run. The drop in my 18V is not allowing the LNBs to change polarity and receive the even-numbered transponders.

One recommended solution was to use RG11 coax which is heavier and has less inherent loss. The other was to use a power inserted in-line amplifier like a ChannelMaster 5216IFD or 5224IFD.

I opted for the latter (ChannelMaster) solution as it is more cost effective than replacing 2000' of cable. I'll post next week after I get the amp and let everyone know how it worked out.

Dave