To the OP: I feel your pain. I have tried several and don't want to spend any more money experimenting. Had a Slime, took it back; junk. The problem I have is trying to fill all 4 tires with 10 additional PSI with a 12 volt compressor is a 45 minute process.
I don't mind spending a little money (once), just don't know what to buy. Yes, there are a lot of them on Amazon, but which ones are the better ones? Anyone have experience with Viair?