Toyota Repair: 88 V6 Pickup CEL Codes 12,42,52, vehicle speed sensor, haynes manual

Question
Hi Ted,
Background:
I have an 88 V6 5spd 4WD pickup w/ 290k miles. I pulled the codes due to the CEL being on and they were 12 (RPM Signal), 42 (Vehicle Speed Sensor Signal) & 52 (Knock Sensor Signal). In addition, when the RPM's are between 1.5k & 2k and you let off the gas and step back on it the truck does what I would call a stumble or hesitation, when you are above or below this range you are fine stepping on and off the gas.

Questions:
1) I have the Haynes manual but I am looking for some sort of guidance/suggestions as to the easy/simple methods to use to check the items first?
2) Do you think the stumbling/hesitation is related to one of the CEL codes?

I appreciate your time in advance.

Thanks,
Ryan

Answer
The main concern would be the codes 12 and 42, the 12 may indicate a distributor problem as the engine rpm signal comes from an input from the distributor, the speed sensor signal comes from the speed sensor on the transmission, the computer needs to see both of these signals without a problem or it can cause driveability issues, the knock sensor code may be due to the other two codes so I would recommend addressing those first, the distributor may need to be replaced as well as the speed sensor on the transmission.