Well, I've never heard of an R/R sensor, either. Based on the symptoms, I
suspect what they've replaced is either the input or output speed sensor
on the transmission. These provide the transmission computer (TCM) with
the important information it needs to shift properly. When the TCM
figures out that it's not seeing the proper information, it puts the
transmission in third gear and leaves it there.
As far as the plugs and wires, if you've got a 4 cylinder, that sounds
about right for quality parts.
If you've got a V6, it's way too low. On the V6, you should put in 6
platinum plugs, and a not-cheap high quality wire set. The intake plenum
needs to be removed to do this job, so it'll have a high labor cost as