You can get more air to the rear passengers by directing some through the under-seat vents, and by aiming the center dash vents between the front seats. The system should be adequate, but if yours isn't cooling enough, I'd skip the dealer (unless you're still in warranty) and take it to an A/C shop. The system may be low on R134a and just need a recharge. If it's a pro shop they'll check it out, charge it if necessary, and add oil and dye as needed.
1995 5.2 ZJ Sold... but still in the family