Volvo: gas milage, volvo wagon, torque converter

Question
I have a 96 960 Volvo wagon.  Last year timing belt idler pulley came off of shaft, engine gone. I replaced engine with a 98 S engine (same as 96). MY 96 got impugn on hwy. and 18 in town. This S engine gets 18.5 on hwy. and about 12 in town. I told Volvo mechanic that it was pulling 2700 rpm at 73 mph and this was to high and should be around 2100 rpm. Acts like overdrive is not kicking in to bring rpm down.
What is your ideas or solution to this problem.
thanks Daniel

Answer
Daniel,
If those RPM'S are too high then all I can think is that the trans is at fault. Have the trans checked for proper shifting and operation. Do you fell all the shifts? If you do maybe there is a torque converter problem, not allowing lock up in the converter. Read the codes for the trans and see if that will help.