I've seen these same problems on Travelocity ("TC") for a while: (a) fares listed when searching by price in a date range but then no calendar; (b) fares showing available with calendar until you're deep into the res. process; (c) selecting one fare, going through the res process, and getting a much higher fare when you get to the actual fare page.

A limited part of (a) on UA flights (at least w. r. t. DEN) is that TC is listing some sort of Ski package rates in the UA published rates. These may be "published" but can only be booked by the affiliated agency offering these packages (don't know who that is).

Problem (c) is more than a tax and booking fee difference. You typically expect in choosing a $200 fare for example that the total fare may be closer to say, $220. What I've seen, and I assume this is the same that whiteknuckles has seen, is that you select a $200 fare, go through the date selection process, and TC shows you a price of maybe $350 and asks for a credit card.

I find TC helpful for their fare listings but I too have experienced too many of these problems to "fight" with TC for a booking for the prices and dates listed if the first attempt runs into these snags.

I also dislike not being able to pick an outbound and return flight segments and have TC give you the best price. There have been times that I was looking to book on 2 different carriers with a combinable fare, but after you choose the outbound flight, TC limits your return options (only to those on the same airline as far as I've seen).