Nissan Repair: 97 Pathfinder service engine soon light, throttle position sensor, mean time between failure

Question
I have a 1997 Pathfinder SE with 152,000 miles on it and the service engine soon light came on yesterday.  I just took the car to Autozone and had a diagnostic done.  The following error messages came up -

P0510 - closed throttle position switch malfunction
P0325 - Knock sensor defective
P0120 - Throttle position sensor
P0732 - Gear 2 incorrect ratio   
P0733 - Gear 3 incorrect ratio
P1705 - Not in P or N during KOEO / KOER

Is it normal for all these errors to happen at once or will some be corrected by fixing others.  What should be done to the car and is it worth fixing?  Any idea on the cost and is it major work or can I fix the sensors myself?

Thanks for your help and Happy Holidays!!  

Answer
William,

With this many miles you are going to have things go out.  So, Mean Time Between Failure has been established to be 100K miles so you are ahead of the game in that respect.  Anyway, the TPS code, knock sensor code, and closed throttle position switch are easy corrections.  Now, the gear problems probably mean you have an automatic and it is slipping ever so slightly.  If you find the cost of a rebuilt transmission to be too much you might think of selling it off.  But, if the vehicle is in good working order it is well worth the cost since the car will run for over 250K normally with minimal maintenance.