I recently installed a Delta single handle pullout debonair kitchen faucet, model # 16927. The installation went fine, but right after turning it on for the first time, the pressure became very low. I fount the aerator where the hose screws into the wand was clogged, after cleaning it out, it was fine for about a week. Now the pressure has dropped again, the aerator is OK, but the water stream coming from the hose assembly also has very little pressure. I have found no leaks, and the pressure is the same if coming for the hot, or cold side. Where do I look next?

Debris broke loose during you install, possible where you shut down the supply water. The aerator caught some debris the first time but now I think you need to pull the cartridge out of the faucet. The inlets are likely getting plugged. I won't bother telling you how to disassemble since you know how to do the install. If I'm worng about that just write back. Many here can help you remove/clean the cartridge.

I disassembled the faucet today, and as I thought, this faucet has a ball valve. All was clean to that point. Guess I will have to go further into it, I really didn't want to disconnect the water lines, but don't know where else to go, any other suggestions?

Did the pressure drop equally for hot and for cold? Probably more on the hot side. My next step would be to shut off and disconnet the supply lines just after the angle stop under the sink. Put a bucket or pan down and drape a towel over the angle stop and open it, if there is debris catch at this point it may come out but you may have to totally remove the stops because logic says the clog will be on the other side of the stop, inlet. This would require shutting down your main.