I had the automatic transmission in my 1992 Honda Accord LX (4 cylinder) replaced with one from a “junk yard.” All work and the selection of the replacement transmission were done by a certified and reliable repair shop. I’m convinced that the fourth gear and overdrive or torque lock-up are not working properly. All gears seem to operate within the normal ranges of RPM/vehicle speed except for fourth gear (the “D” gear). On a flat, level freeway driving at 65 MPH the engine RPM is 3100. Is this normal? The repair shop folks are vague. One of the mechanics said that they used a transmission from a Honda Prelude and that it was the same as for the Accord. However, the shop owner said that it was an Accord transmission. Did I get either the wrong transmission or a faulty one? What should be the RPM at the above mentioned cruising speed?
That rpm seems a bit high, but not too far off from what my '03 Civic is turning at 65mph. A Prelude could have the same transmission, but it would likely have some different gear ratios. The Prelude was a “sport” car and that would mean different gearing than a standard Accord. If the transmission was from a Prelude I’d suspect a higher final gear ratio and that would mean higher rpm’s at cruising speed compared to the original Accord transmission.
Make sure the transmission is going into 4th gear and then there should be another noticeable drop in the tach indication of motor speed when the torque converter locks up. Torque converter locking up would drop the rpm about 300 rpm in that car.
What was the rpm at 65 before with the original transmission ?
You should be able to feel the shifts in this transmission, three for gear changes and one for the torque converter lock up. You could also have someone else drive while you watch the tach, or have someone else watch the tach to see if it make the required number of drops.
Just for reference, we have a 97 Accord LX and it turns 2450 rpm at 60 mph.
I seem to recall that my '92 Accord also revved at ~2400 RPMs at 60 mph.
The OP can check whether the trans is actually in 4th or in 3rd by doing the following:
On a level road, bring the car up to 45 mph or so, and stop accelerating. Just hold it at that speed.
By 45 mph on a level road, the trans should be in 4th gear.
Now, move the shift lever to the 3rd gear position.
Does the tach show a considerable RPM increase when you downshift?
If not, then it is very likely that your trans was already in 3rd, and thus, did not downshift when you moved the shift lever.
As Keith mentioned, it is also possible that your trans is in 4th gear, but that the trans is not going into torque converter lock-up mode. However, this problem would not lead to as drastic a difference in RPMs as failure to shift in 4th gear would.
Assuming the Prelude was from the same model year era as your Accord, a Prelude transmission shouldn’t be problematic. They both used the same motor, the F22-A. That RPM does seem high, but it might be in line with the prelude transmission IF the transmission is from a Prelude Si. The Prelude S and the Accord had the same fifth and final drive ratios. The Si was geared more sporty and turned 3366rpm at 70mph as compared to the Accord, which turned 2782rpm at 70mph. (the VTEC model was geared even more sporty, 3610rpm at 70mph, but I don’t think you’d gain 500rpm in just 5mph - not that I would be a reliable source on doing the math to figure that out 
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So it would seem the shop decided to give you an Si transmission (again, assuming they took it from that generation of Prelude). Were I you, if this bothers you, I would tell them that you wanted your original spec transmission, which means one from an accord or a Prelude S, not a Prelude Si.
A twenty year old car and a junk yard transmission…You pays your money and you takes your chances…
Not long ago we had the same question on here. It seems to me that we found out that 3k RPM should run you about 67 MPH. That was a Honda also.