Hello and welcome to JustAnswer!
Are you running it on recirculation when you are checking vent temp?
What is the temperature outside when you are checking the vent temp and pressures?
Is the recirculation door present and working?
Ok. It sounds like your vent temperature is about in line with what I would expect it to be at 90 outside without recirc, but your pressures are a little low for temperatures that high. Any time you check vent temperature you have to have it on recirculation, blower motor on the number 3 position. At 90 degrees outside you should be seeing about 55 degrees out of the vent by the book, with it on recirculation and the blower motor on the third position. At 90 degrees ambient the low side pressure should be 30-40 psi and the high side should be 250-350. Even though your vent temperature is in acceptable range the pressures are pretty low for 90 degrees outside, you are low on charge. I would have it evacuated and recharged and you should see a drop in vent temp, and be sure to use the recirculation function when you are running the a/c.
They don't give a nice big graph anymore, you have to estimate if you are in between. I tried to upload it to you but it seems we are having site problems and I can't upload pictures at the moment. I'll try again in a couple minutes.