If you got low pressure, low flow G.P.M. and you want to fix the poor design. This is not counting the possibility of a valve that needs to be replaced, leak in a lateral, partially open water supply.
The Toro Precision Nozzles are better than the hype. I recently had a .5" supply and had to design and install sprinklers on a budget. The nozzles were more expensive, but they saved me timer size, pipe, and wire. I am not a walking commercial for toro nozzles, but wow.
I am just saying for what it is worth.