Low Flow in Shower

Hello, I have a flow problem in my shower head that is compounded when another faucet is opened. I measured my static pressure at the shower head at 60 and it dropped to 50 psi when I flushed the adjacent toilet. The drop in psi is slightly more when I have the shower head mixer in Hot setting. I proceeded to remove my shower head and I opened the shower head mixer in Hot only and then Cold only. I noticed that there was less flow when in HOT. I have municipal water coming in through a meter 5/8" and 3/4" out. My line to the house is 3/4", the electric 50gal water heater is 3/4" also. My branches are 1/2" line. I suspected the main valve but that checked ok. Since the problem is more pronounced with the hot water I proceeded to check the Water heater. I drained some water out of it and it had some sand which was cleared after draining a gallon or so. I am not sure if the water meter has a PRV. This is Florida , Osceola county city water. I dont think my lines are clogged Since my house is copper pipe and was built in 1986.
I am puzzled , can anyone assist me with this situation?
Thanks
Tneg