I always feel that under GH, liverpool seems to tired out very easily because we play more defensively. Under Rafa, we seems to improve slightly, except for those matches after CL. If you look at the stats of matches we played after CL, you will relise the problem is prob with Fitness and Fatigue rather subbing for Pelle as pointed out by 
giddygoat. 
 
We have conceded many late goals this season, think Chelsea, Everton (almost draw that match after 2-0 up), Southamption etc. All these are most likely due to fatigue. You can sub for 3 players but all 11 played in CL so no choice but to play a few as starters.
 
As for consistency, i think you cannot judge Rafa on this season. Given our injuries to Cisse, Pongolle, Baros, Mellor, Kewell, Hamann, Gerrard, Garcia, Alonso, Smicer, Nunez, Kirkland and god knows who else i have missed out. Plus the players that we sign this year like Carson,Alonso, Nunez, Josemi, Morientes, Garcia and Pelle.
 
Not forgetting 1st team players who left on loan/sale such as Owen, Heskey, Murphy, Diouf, Diao, La Tallec and Henchoz...
 
I think we have done remarkably well. Kudos to Rafa. I do think he has in mind his 1st 11 and prob the 5 subs. Maybe i can second guess....
 
Keeper: Dudek (R: Kirkland)
Defenders: Finnan, Traore, Hyypia, Carragher (R

elle)
Midfielder: Riise, Gerrard, Garcia and Alonso (R: Biscan, Hamann)
Attacker: Morientes, Cisse (R: Baros, Kewell)
 
Actually i will fancy the above team to play against any team and do well if we are in full strength. Of the above, maybe Dudek, Finnan and Traore can be replaced with better players. The rest are all top class internationals. Too bad we have so many injuries.