I trained at 7000+ feet for five years.
There are several factors in place here. The first is adaption and having your body and mind get used to training at altitude.
You're an experienced runnner-so it will take some time mentally to adjust to slower interval and tempo times. You will adjust and get better at hitting faster training paces. All I am saying here is that there is a mental adjustment.
Each workout type is a little different. There are subtle differences between atltitude's affect on a 4 v. 6 mile tempo.
Intervals are a challenge and you will have to adapt to the extra time it takes to recover in between. Breaking workouts down into sets is sometimes a good approach.
Reps--if you are taking full recovery--take full recovery.