Buying a new rig won't solve the problem if you are staying in a state with high temps. :B
You have to start covering and insulating for it to be cooler inside.
I slip van size windshield sun shades under the day night shades on the side the sun is coming in. I put RV vent pillows inside all the roof vents, these vent covers are THE most important part of keeping it warm in winter and cool in summer. You will be shocked of the difference when you put them inside the roof vent opening.
Put awning out and down in lowest position when sun is on the side. You can pick up 10 15 degrees just doing the above.
When I decided to stay in Florida during their sweltering summers I added black limo tint to the windows. THAT made a huge difference. I used the 'removable' limo tint from Walmart because I didn't want them permanently on the windows. I ended up leaving them on and they look like they were professional done and are going on 4 years now and look like the day I put it on.
Yup, the first time you stay in one of these southern state you have to get educated real quick on how to keep an RV cool. Because your ac can't do it alone without some help from you.