I replaced the upstream O2 sensor in my 2000 4.0 Ranger. When I reconnected the battery and tried driving it, the transmission shifted hard and the truck had no power. It drove fine in reverse though. The CEL is still on as well. I don't think it matters, but I replaced the oul as wellbefore I statrted it back up Has anyone had this issue before? Is it a faulty O2 sensor?

 

Welcome to the forum

Why did you replace just 1 upstream O2 sensor?
Was there a code, and what was the exact code?

O2 sensor can not be used until it is heated to above 650degF which takes about 4 minutes from cold start, so if engine lacks power cold then not an O2 issue, it's not being used by computer
O2s are also ignored at WOT(wide open throttle), so if after warm up engine runs better at WOT then could be O2 issue

A code that mentions O2 sensors usually means the O2 sensor is working, the code is telling you there is a engine problem, an air/fuel mix problem usually

So need exact codes before and now if there are any new ones

 

Just pulled the codes:

P1451 FORD - EVAP Control System Canister Vent Solenoid Circuit Malfunction
P1747 FORD - Electronic Pressure Control Solenoid 'A' Short Circuit
P0743 FORD - Torque Converter Clutch Circuit
P0750 FORD - Shift Solenoid 1 Circuit Malfunction
P0755 FORD - Shift Solenoid 2 Circuit Malfunction
P0760 FORD - Shift Solenoid 3 Circuit
P0765 FORD - Shift Solenoid 4 Circuit
P0135 FORD - O2 Sensor Heater Circuit Malfunction Bank 1 Sensor 1
P0155 FORD - O2 Heater Circuit Bank 2 Sensor 1

 

These are all caused by a blow fuse most likely, check Fuse #13 in engine bay fuse box, 15amp

"Looking" at a fuse can't tell you if its good or bad, test it with ohm meter or change it with new one

Turn on the key, count to 10, then turn it off, check fuse again to see if it blew again, if so you have a shorted wire in that circuit