We just went through this... 30 year old house that had never had central AC... So add the price of running ductwork and new copper lines and your $5700 quote suddenly looks like a bargain. Ours came in just under $10k for a 2.5 ton system. We are in Florida.
As far as your immediate problems, have you checked your coil to see how dirty it is? IIRC correctly, dirty coils can cause the system to run harder due to lack of airflow through the coil. System runs harder, current goes up. Or maybe I'm just making that up. I guess my point is you're on the right track checking/replacing the cap but also check the cleanliness of the system to keep it healthy and prolong its life too.
As for brands, Daiken recently bought Goodman to gain a foothold in the US market. Daiken is a Japanese company and supposedly the largest refrigeration company in the world, or so I was told. It was explained to me that the Goodman line will be maintained as the entry level line, and Daiken will be marketed as the premium line. Daiken is supposed to be working wonders for increasing the quality of Goodman. We had Daiken, Trane and Carrier quoted. Daiken had a better warranty and more features for the price but the contractor didn't run a heat load calculation on my house (I did) and our sizing didn't agree. I've had Trane's in past houses I've owned and never had an issue with one other than a capacitor but again, same Contractor as Daiken. I had two other contractors quote the job, both of which were Carrier dealers. One of them did a proper heat load calculation and arrived at the same size and me. They won the job. I would have gotten more quotes but we were tired of sleeping in 85+ temps (window shaker had failed). So we have a Carrier. So far so good, but we are only 3 weeks since turn-on. It has a variable speed air handler with controllable humidity setting which is pretty sweet.
Good luck nursing yours along and may it last the rest of the summer for you
