Looking for some suggestions to improve network capacity

Here is our problem:

We are in an area that is to sparsely populated for dsl or cable, but still have quite a few homes in the same area. currently we have 1 full 900 cluster and 2 more 3 ap clusters both facing south to the bulk of our customers, most of the southern 180 degrees worth of AP are near capacity 30 35 SM on each AP
Needless to say this is starting to turn into a problem and we have stopped installing 900 customers to the south.

We have a 2.4 cluster also, but the trees stop us from using them in most of the installs, we have not tried the new 400 series yet and we are hoping someone here had successfully used the 400 series to get some load off of 900

60 to 70% of our customers are 1.5 to 4 miles from the tower, and we have been trying to find a place to build a second tower 3 to 4 miles south of our current tower so we can add more 900 to our network, but I am still concerned about self interference between the two towers.

All APs are integrated. Our SMs are 75% integrated, 10 to 15% more are SMC w/ yagi antennas and the last few are indoor

Thanks for the input!

build another tower, use cmm.
900 is the best for going thru trees

Do you have 900MHz customers with LOS that could be converted to 2.4?

What are your SM QoS settings on your 900 AP’s?

You could go to narrower sectors - i.e. split a 120deg sector to two 60deg sectors. You would not only gain capacity but distance as well. Would take some judicious use of spectrum.