RANGER for repair

Today I sent my RANGER to Ford SC (auto connextion) near federal highway, I felt the ranger was losing some power and torque was low. There's a jerk before gear change. Particularly for low gears (1st-2nd). Fearing for my transmission, I called my SC and was asked politely to send the RANGER to them.At 11am, the SC jack up the RANGER, and I went under to inspect, accompanied by the service technician. The technicial tried moving the universal joint. The Universal joint is made of three separate joint connecting the shaft to the back wheels. These joint was loose. It cannot be tighten. This was due to wear and tear as they explained it. My ODO shows 45,000km. The next Ranger that came in had same problem at 47000KM. From WIKIPEDIA, A universal joint, U joint, is a joint in a rigid rod that allows the rod to 'bend' in any direction, and is commonly used in shafts that transmit rotary motion. It consists of a pair of hinges located close together, oriented at 90° to each other, connected by a cross shaft.When we accelerate the torque spins this joints causing wear and tear, That's also a reason the low gear suffers more. I actually feel the car jerks at low gear, low speed. I was informed that I need to change, not service, not re-inforce these 3 joints. Luckily the joints for my 4x4 system was still good. It's the three Universal-joints for the 4x2 that gave up. I'll tell u the cost later as the RANGER is still in SC as I type. p.s: That's why cleaning my KNN did nothing.