You sound like you're on a typical outdoor clay track.
Dry/dusty/groove tries to form but can't during the day.
Moisture may rise at night and it goes tacky and/or slick depending on the amount of moisture.
Of the Losi tires, the G2 Digits (regular digits; NOT ultra) work great all around and drive much better/more consistent than PL Calibers.
Or, of the JC tires, try Crowbars/Crossbows if you want steering and loosen the car up a bit in the rear. This drive similar, but has a bit more steering and is "sharper" handling than the Losi XBT/Eclipse Combo. The Losi XBT/Eclipse is smooth and easy to drive overall and I use it a lot on outdoor tracks like what you described.
JC Hitmen are like the older version of Crowbars. They have a neutral feel, very predictable.
Of the tires you have, you could try running Cityblock/Ibeams (beams on rear) during the day. I've never liked CB on buggy though, they don't have enough turn-in for my taste.