I've got a 13 year old home, we purchased in October of last year..

It's approx. 2100 SF... There's nothing remarkable about the house, just seems to be a very well built and VERY well insulated (tons of insulation in the attic) home...

The problem is the heat-pump, or what I think is a problem, so I'm asking for some advice...not knowing anything about heat pumps..

For starters, I keep a fresh/clean filter in the unit, and check it often..
I've learned that lesson already..

The heat pump is very quick to "freeze up" on us (the coils in the house) if I set the thermostat lower than 75 degrees...

Right now, it is almost 100 degrees outside (Waco, TX) and it is just happily humming along at it's 75 degree setting, cooling the house to 75 degrees, cycles on and off once in a while and does okay...at 75 only..

If I set it to 74, or any lower, the inside freezes up...and I've got to thaw it with the fan..even at 75 degrees, ice is beginning to form on the coils..

This occurs even at night. Our previous home (air conditioner equipped) I got used to sleeping in a cool house at 72 degrees or so..

Even at night, when it is 75-78 outside, I set this heat-pump less than 75 degrees, it freezes up..

It just seems like it's on the "verge" of freezing at all times..and I find that frustrating..

I've had it serviced twice, and the tech said everything is functioning as normal, and if anything, the a/c might be a little undersized for the home, and the blower on this particular model doesn't "push enough air" or something like that..but that's all he could tell me..

Is it too much to expect a heat-pump to cool the house down to 72 degrees at night on an 80 degree night when I want to?

Friday night, AFTER installing a fresh filter, I set it to 73 at 11:30 at night before I went to bed...only to be woken up to the sound of it humming as it was frozen again at 3:00 in the morning..

Is that asking too much?

Do you think my unit is undersized?

Do they lose efficiency over time and I just need to get a new one?

If so...how much should I expect to pay for a new unit inside and out..?

OPINIONS?
ADVICE?