I changed my kitchen cabinets,sink and faucet.I had to unsweat the pipes as they came up through floor.The pipes I took off had a tee.Going out the top was a shut off valve to where the faucet hooked to.Off the other side of the tee was a 90 degree with a 12 inch rise.I replaced pipes without the rise.Now the water pressure is low.Has that got something to do with it?

You mean the water flow out the faucet is low if that is the case, remove the Aerator see the Image below try the water if the flow is good, clean and install the Aerator and you will be OK, if the water flow with out the Aerator is weak you may have problem with your faucet or the angle valves, click back and some one will help you, Thanks.