1996 Jimmy AC

Living in AZ makes AC a necessity. Put a new compressor in this spring. Checked charge level - seeing about 55 psi on low and about 280 psi on high on a normal day (about 105°F). System works adequately on cool nights and mornings when temps are 80°-90°. But drive around during the day after leaving the garage at the house and it just slowly goes downhill. Get a burst of hot air pulling out from stop lights - like the compressor is cycling off. Never was a kick butt system but definitely worked better years ago. What am I missing? Thanks!

Just repalced my compresser works fine. took three small cans