coolant temperature sending unit

[Red_Rider_00]

2001 XLT 3.0 flex fuel automatic. Check engine light caused me to code read which said ctsu or ct switch. Replaced both, light still comes on. So then went ahead and upgraded to Summit water temp gauge which came with it's own sending unit which goes in place of factory unit. I ran a dedicated wire from unit to gauge. Factory sending unit wire and harness are tied up out of the way. Under hard accelleration engine stutters until about 3,000 rpm then catches and runs hard to redline. I just wonder if I splice the factory harness from ctsu into the Summit wtgsu if the unit will run both systems. They each only use one wire. I believe this factory wire being unhooked may be the cause of stuttering. Any ideas? Thanks P.S. also run a Summit 4 in. tach in addition to the factory tach and I simply spliced the Summit tach wire into the factory tach wire and both of them work fine.