Losing my Tempo

Have had 3 runs since last post, here they are not in chronological order.
Tuesday: 10.3miles @7.14min/mile AvgHR 144bpm, felt good th'out
Thursday:10.2 @7.33min/mile AvgHR 142bpm, never got going.
Wednesday:

Had planned on doing another interval session, untill I read this article http://www.pfitzinger.com/marathontraining.shtml , which suggests that tempo runs are better than intervals when training specifically for a marathon. Seeing as I don't have access to a track at the moment this was music to my ears. I still think I will do some interval sessions as I do want to be improve over shorter distances as well, I'll just combine the two of them. The pace suggested was current 10mile race pace. My last 10miler was 59.30 so after a two mile warm up I attempted to maintain just under 6 min/mile pace. In short I failed, dunno if I was just tired or lacking the necessary adrenaline or is that my racing shoes really do make that much of a difference, I don't know. I managed 4 miles with the following splits: 5.55, 6.05, 6.07, 6.06, followed by 2.5miles cool down. I guess normally before a race I won't have ran over 18miles in the previous two days...