You should have NEVER married an old R22 air handler with a R410 heat pump. The equipment inside and outside should be matched. Not to mention you have to get ALL of the R 22 oil out when going to R410 and almost impossible to get out of the air handler installed. Not to Mention R 410 uses larger copper line sizes, which your R 22 air handler IS most likely not going to have.
Your temperature differential should be about 20F which it's not. You have issues with the installation.

I can see that house needing 2.5 tons because it's uninsulated.

MAKE sure they replace the copper lines to the appropriate size for R 410 from condensor to air handler, make sure they also flush the condensor REALLY well and put the appropriate oil in the system, and vaccuum the system really well before charging it.

So did you get your install fixed?

Don't want to jinx anything but installer tech and helper finished installing the air handler. Although old 2.5 ton air handler was replaced with a new 2.5 ton air handler, the newer one is dimensional different. Biggest issue was a height difference. More than minor carpentry rework was required in the closet. Took them ALL DAY and what with my demeanor, they went above and beyond to make it right.

The old line set is the proper size for R410A ... 3/4 suction line and 3/8 liquid line (for 2.5 ton) ... and was not replaced. It was flushed with R11 refrigerant and nitrogen.

Once the system was lit off with a new heat pump AND matching air handler this afternoon, the suction pressure was 20psig high and more importantly, the subcooling was 18.5 rather than the 12-14 it should have been. The issue was attributed to the tech that added 1.75lbs of R410A on Monday evening.

Once running for ~15-20minutes a little refrigerant was recovered and pressure readings fell right into spec.

95 degrees outside and air coming from the kitchen vent is 56-58 degrees. Probably 4 degrees cooler in the duct right above the air handler. Attic is hot and air heats about 4 degrees from the air handler to my kitchen vent, but my kitchen vent is where I as a homeowner have always measured air temp and right now it is as good as it has ever been at 56-58 on a very hot day. Oh, thermostat is set to 79 and while I could turn it down, am comfortable.

I wouldn't let them leave today until I saw pressures and temps in spec and we are there now.

All is good. Cooling is great. Will find out about heat in 2-3 months. Looks like my HVAC journey is over ... COOL

Thank you all VERY MUCH for the help and advice. Greatly appreciated !!!

Sounds like all is good. If cooling is working like that, heat will work just as well.

I'd highly considering getting fiberglass insulation blown into your attic, it will pay for itself in less than 6 months.

An HVAC tech other than the installers called me at 7:35 this morning. Said he just wanted to drop by and check heating & cooling system operation.

All still looks good. 21 degree air temp differential wet bulb to air at the plenum.

R410A numbers, pressure and subcooling, are in spec at the heat pump.

While the system had run for 15minutes to get good pressure and temp reading, I noticed the temp at the air vent in kitchen was fifty (50) degrees. That is the coldest air I've ever seen from that vent.

This 2.5 ton beast will freeze me out if I allow it to. COOL

I had mentioned to a couple of people that I thought a reputable heating & cooling company would send a top tech over to verify new system integrity and new customer satisfaction ... and Woodall Heating & Cooling did just that this morning, without a call and request.

It's been a journey with the old and the new but I'm a happy camper now.