Transmission/Check Engine Light/Speedometer

First thing to check would be the trans oil level
To little oil will cause it not to shift
And worse case the torque converter needs replacement

can try a filter change but issue can be in the valve unit --pump --or simply worn clutch packs

Best guess :Check the speed sensor on the transmission, these fail.

some also have a transmission computer on the firewall that interfer with driving down the road if they go bad it will cause vehicle to downshift and go slow and then go no where until it cools down then it will crank and go again.

you have checked the fluid level right?

Try checking your timing to solve the ping problem, your timing might be too far advanced. For the downshifting problem, I have this same issue on my odyssey, On the top of your efi manifold you will see 2 wires that control your throttle, One of them extends to the transmission and basically lets it know when you are pressing firmly on your gas pedal, telling it to downshift. I would adjust it so the cable has some more slack in it, therefore requiring a harder press on the pedal before downshift, and hopefully a sooner upshift. You can also slightly adjust idling problems if the van is running high while in park or drive while sitting. As for the gas vapor purge code, I would first try replacing the egr valve, its only a couple bucks and takes no more than 5 minutes.

If the speedometer suddenly drops back and then returns to being close to your actual speed and the transmission shift or acts up at the same time this is happening then you may have a failing Vehicle Speed Sensor, usually refered to as a VSS. This sensor tells the engine computer, instrument cluster, and transmission controller how fast you are going so the controller can select the proper gear for the transmission to be in. If the speed signal is lost, wrong, or erratic then the transmission may make a quick downshift to to try and match this new, but incorrect, speed and then may make an equally quick upshift to rematch the correct speed once the signal is correct again. This should be an easy one for anyone with a good scan tool to check out as the actual speed reading signal can be observed during a test drive and it's usually pretty easy to spot the glitches. Good luck, hope this helps!

first off if the car is still moving backwards it will not enguage drive untill completly stopped [mentioned this in case you didnt know] there may be a new transmission program for the other problem. call dealer and ask

no codes found because your checking the PCM,
your problem is you need codes from the TCM,the computer for the transmission,since you replaced the speed sensor the other two things that affect a speedometer and transmission are the input and output sensors,they both screw in the transmission.

have your transmission checked by a professional, It sounds like you have a shift solenoid going. Had something similar on a van. I don't know where it is on your vehicle so I don't know how deep into the transmission you may have to go.