I was in same boat....my system was continually needing band aids, would run nonstop on 90*+ days, and my summer electric bills were skyrocketing.
Quotes for replacement were above $6k for a 4T AC and 100k BTU gas furnace, attic installation.
I went through Factory Furnace Direct and got the Goodman furnace, compressor, and condenser, for right at $2k delivered. Paid my normal HVAC tech $1k to do it as a side job on a weekend. So I was real happy that I was able to do it for half of the lowest quote I got.
I was a little nervous about Goodman since I don't know anyone with that brand and don't see it used around here. So I asked my tech and he said that's what he used at his house and their stuff was good as any. That was good enough to put me at ease. I debated paying more for higher SEER and he talked me out of it. A lot more maintenance and potential for water damage in an attic installation. So I ended up getting 14 or 14.5 SEER - whatever the lowest we're supposed to install in our region.
I can't be happier with it and am glad I saved the $ not going with higher SEER. even at 14/14.5 it is MUCH more efficient than original Lennox (from 2003). Quieter, cycles off even on hottest days, and my summer AC bills reduced by more than 1/3! Furnace - well that seems same. gas bill is same. Only thing I notice there as different is the air handler is quieter. But I didn't have problems with original one and tech even told me not to replace it since nothing wrong with it. But I figured if ripping stuff out anyway and adding furnace is tiny cost on the package deal, may as well have peace of mind that it's new and under warranty....
I don't know what your min SEER rating needs to be by code/gov't mandate, but my guy showed me the math and flawed reasoning. I was thinking if X higher SEER saves $X every month, it pays for itself. BUT I wasn't considering I don't run the AC 12 months a year, but was doing the math that way. He said really it's only saving the most in the 2 maybe 3 hottest months of the year. Will be the same in transitional months, and of course $0 during winter. Redoing math that way, then figuring slightly higher installation costs, higher service costs, the higher SEER was actually more expensive over 15-20 yrs even though my initial math/reasoning made it seem cheaper in long run.
Anyway....all that to say, if I had to do it again after using the system for over a year now, I would definitely buy a Goodman package again on my own and then find a tech to install "off the clock". Still get the factory warranty - you just have to register it yourself with Goodman. I have no affiliation with Factory Furnace Direct, but while researching what to buy and from whom, they were who I ended up choosing as other places advertised items they didn't physically have in stock and true ship dates were estimates. And when I called these guys at ordering time and told them I had a lower quote elsewhere, they beat it by $1
I reused existing lineset and ductwork since tech said nothing wrong with them. Oh, my house is in full sun with 0 shade and faces south. Not really well insulated, octopus flex ducts from the attic, basic double pane windows, and I could make a lot of improvements on general air leakage. House was built at height of housing bubble in 2002 in a housing plan and the developer definitely cut a lot of corners and tried to put up as many houses as quickly and inexpensively as possible. 2700 sq ft, one zone for AC. And my worst electric bill last summer was $190 with us keeping thermostat on 72*. So I can't complain at all about my choice for lower SEER and lower price brand name.
