I bill for PT, but we do not accept United so I am not very familiar with them.
However, some ins co will only pay for one eval (97001) in a set amount of time. One ins co will pay once every 18mo! even if it is a different problem, and by law the PT has to do the eval! Others will only pay for the eval on the first visit and no other treatment.
Normally, you would not need a modifier if you only charged the 3 units. If you charge more than 4 units (for example 2-97140 and 2-97110 plus 97001), many ins will only pay for the cheapest 4. I would call United and see what they say.
Good luck