Heat Pumps and Electric Heating - always running

I recently installed a temp-rite heat pump 8050C thermostat. It seems that the hp never reaches the desired temperature since i installed it. the auxillary coils seem to work when they are on as the heat increases. The unit seems to be running all the time in regular hp mode, blowing colder air, not really warming the house to the desired temp (70F) I would have to say it is about 3 degrees lower than where i want it.
Is there any thing i can do to test that things are working correctly?

I have a Lennox HP and my White-Rogers thermostat died. It had a failure of the internal relay circuit so it wouldn't turn on the blower relay. The HP works perfectly otherwise. It is about 6 years old. My original HP lasted 13 years. The W-R was used with both of them and was installed about a year after we built the house.
I went to Home Depot and bought an 8050C like yours to replace the W-R. It works EXACTLY the way you describe. If I set it for 70 F, it will run until 70 is indicated for a minute or so and then will drop below 70. The unit will remain running until the next program time that changes the setting lower. As an experiment, I adjusted the temp to 74 F. Sure enough, the system ran until it reached 74 for a minute and then dropped to 73 and remained on so it isn't a problem reaching 70 per se.
I had a service tech come look at the system since we are having extreme cold in the Dallas area right now and I wanted to make sure there isn't a problem. I'm now poorer and the HP is fine.
I think there is a design problem with the 8050C in HP with aux heat mode. It is the only thing I can think of that explains it. I intend to return it and hopefully find another White-Rogers. That original programmable thermostat lasted 18 years so they must have their act together.
If your system was working correctly before you changed the t-stat then I think it would be prudent to return your Rite-Temp as well.
Michael

We tell people that with the heat pump. Set the tstat and let it alone. It cost you more to gain back the temp you lost with the set back programmable thermostat than you saved. if the big copper line is not real warm when the pump is running. Best to go to EME for a time. Till the temp outside goes upabove 20o

Well, I replaced the 8050C with a Honeywell RTH7400D. Operation is back as it was before with proper cycling and the temp outside is still 30 F. This proves to me that the 8050C has a design flaw or the one I bought is defective. I believe the design flaw is more likely.

Aux heat doesn't come on every time the system cycles so emergency heat isn't really needed at this time.