I don't think Amtrak guarantees connections of 2 hours or less, so take that into consideration. I just made a test booking from Harrisburg to Denver (because you're staying in Denver for a day) using Amtrak's interactive travel planning map and it gave me a 3 train route as follows:
Segment 1 of 3
Harrisburg, PA, (HAR)
43 Pennsylvanian
2:36p, Tue, Jul 12 (5h 23m)
Pittsburgh, PA, (PGH )
Union Station
7:59p, Tue, Jul 12
4h 0m connection in PGH | Transfer
Segment 2 of 3
Pittsburgh, PA, (PGH)
Union Station
29 Capitol Limited
11:59p, Tue, Jul 12 (9h 46m)
Chicago, IL, (CHI )
Union Station
8:45a, Wed, Jul 13
5h 15m connection in CHI | Transfer
Segment 3 of 3
Chicago, IL, (CHI)
Union Station
5 California Zephyr
2:00p, Wed, Jul 13 (18h 15m)
Denver, CO, (DEN )
Union Station
7:15a, Thu, Jul 14
Then I made a test booking from Denver to Portland and got:
Segment 1 of 2
Denver, CO, (DEN)
Union Station
5 California Zephyr
8:05a, Fri, Jul 15 (31h 8m)
Sacramento, CA, (SAC )
Sacramento Valley Station
2:13p, Sat, Jul 16
9h 36m connection in SAC | Transfer
Segment 2 of 2
Sacramento, CA, (SAC)
Sacramento Valley Station
14 Coast Starlight
11:49p, Sat, Jul 16 (15h 51m)
Portland, OR, (PDX )
Union Station
3:40p, Sun, Jul 17
And finally, a fake booking from Portland to Harrisburg gave me 2 choices: one was a 3 train trip and the other a 4 train trip. I'm showing below the 3 train trip.
Segment 1 of 3
Portland, OR, (PDX)
Union Station
28 Empire Builder
4:45p, Tue, Jul 19 (45h 10m)
Chicago, IL, (CHI )
Union Station
3:55p, Thu, Jul 21
2h 45m connection in CHI | Transfer
Segment 2 of 3
Chicago, IL, (CHI)
Union Station
30 Capitol Limited
6:40p, Thu, Jul 21 (9h 25m)
Pittsburgh, PA, (PGH )
Union Station
5:05a, Fri, Jul 22
2h 25m connection in PGH | Transfer
Segment 3 of 3
Pittsburgh, PA, (PGH)
Union Station
42 Pennsylvanian
7:30a, Fri, Jul 22 (5h 20m)
Harrisburg, PA, (HAR )
12:50p, Fri, Jul 22
So this last booking looks like they will guarantee a 2 hr-25-minute connection. By the word "guarantee", I mean that if the train is late such that you might miss the connection, Amtrak will either hold the connecting train until yours arrives, bus you to the next destination or pay for a hotel until the next appropriate train comes. Before I even knew about guaranteeing connections, I would book my segments totally separately. One fine day, the LSL was 5 hours late into Chicago due to a trespasser fatality which would have caused us to miss our connection (SWC) by 30 minutes or so, but because the LSL had a number of passengers on it that did have the guaranteed connection, having booked their trip properly unlike me, Amtrak held the SWC in Chicago until the LSL arrived and we made the transfer huffing and puffing away (Hurry, hurry!).