Pump losing prime over time after installing heater

I have an 18x36 cement in ground pool that holds approx 30k gallon. It came with the house when I bought it so I figured I better learn about pools. The only thing I have learned so far is that they are flippin expensive. Anyway, I added a Hayward heat pump:

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

I also rebuilt the 3/4 hp motor that had been chugging since 1989 (kept all the origianl plumbing intact). This system (minus the heater) worked splendidly last year, but now it will not keep prime. I went to clean the filter and saw there was NO sand in it. Instead the previous owner had filled the sand filter with DE. I changed all that and made it right so that is no longer an issue.

After everything was recitified and connected I primed my pump, got it started, watched it never really reach full prime, and then went back out in 2 hours to find the brand new pump running dry. I have not found leaks with shaving cream or watching for spray when I shut the system off. I thought maybe the motor is too small for the system now and thus exaggerating some leak somewhere because it cannot pull the water. Maybe I am wrong. Pressure hangs at about 20 psi on the sand filter.

Head:
2" pipe everywhere
required flow = 63 GPM
linear feet of schedule 40 2" pipe = 158'
number of 90's = 20
add a sand filter, and suddenly I am in the stratosphere with head loss.

Do I look for a new filter/pump system?

where do I start?