St. Augustine is pretty nice. Not as invasive as bermuda plus I don't think it needs as much water and sunlight as bermuda.

Replacing your lawn may not solve the problem.

The most common cause of brown or dry areas in lawns is the sprinkler heads. Over time they can become clogged, chipped, or tilted. There could also be a change in water pressure that will reduce the length of the spray.

An easy way to see if water is the issue is to run your sprinkler system and then wait about an hour. Use a long screwdriver to push down into the soil in various locaitons. It will be easy to push into moist soil but very hard to probe dry soil. This will show you the areas that aren't receiving enough water. Next, place tuna cans (or any short can/container) and place them on your lawn. This will show how much water (and how uniform) your sprinklers are putting out. Turn on your sprinkler system for a given period of time and then measure the amount of water that collects in the cans. The amounts should be the same, but seldom are. This time of year Bermuda lawns need 1-1/2 to 1-3/4 inches of water each week.

The solution? Replace the spray heads. Its easy and fairly inexpensive. Look for spray heads that will reach the adjacent sprinkler so you will have 'head-to-head' coverage. This could be 6, 8, 10 or more feet. There are new spray heads on the market that use streams of water rather than misting sprays. They are 30 percent more efficient and are called 'stream rotors'.

Your lawn could have a buildup of thatch. This is a tightly intermingled layer of dead and decaying turfgrass tissue derived from leaves, stems, stolons and roots. Leaf clippings contribute very little to thatch accumulation. As thatch accumulates, there is a tendency for root and rhizome growth to occur primarily in the thatch layer rather than in the soil. This results in a weakened, poorly rooted turf that is prone to stress injury and requires frequent irrigation and intense management.

You can check for excessive thatch buildup by digging a pie-shaped wedge of soil from your lawn. The thatch layer will look sort of like potting soil and if it's thicker than 1/2 inch you should dethatch your lawn. Do this now so that your grass has a chance to grow back before fall.

Here's a link to information written by Dr. David Kopec from the Karsten Turf Research Center at the University of Arizona.

Here is a link that might be useful: Lawn Information

I agree with aztreelvr. Unless you figure out why you've got the dead patches now, you'll have the same problem even with the new sod. You've got a problem that's not going to go away with new sod.

Fix the water issue(if there is one) fertilize and Bermuda will fill in by itself. If you don't want to wait then sod it. Are you using a reel or rotary mower? How many times a week do you want to mow? Rotary mower go Bobsod. Reel mower go Tiff of Paspalum. This time a year you should mow twice a week

Fertilize & check irrigation , use a good fertilizer i usually use turf royal or fertilezona brand fertilizer.(19-6-13)First rake out brown spots and remove as much material as possible then Fertilize.Water twice a day for 7 - 10 min for a couple weeks until lawn greens up and fills in. Hit the grass with a second application of fertilizer two weeks after first one. *Make sure you let sprinklers cycle through immediately after all applications of fertilizer other wise you will burn grass if not watered in! I have revived lots of horrible looking lawns following these steps.