Not hitting second gear

clean your air cleaner filter.

Check the Flyback Transformer and Hot. especially if its a soft ticking sound

Change your clutch shoes and spring, if shoes are still good,then just the spring

when deactivating youre four wheel drive make sure youre rig is in nautral this helps with the gears lining up. whan youre 2-hi light flashes hit a second time. Ive had this problem befor.

sounds like 3rd gear/clutch is worn.I don't think a service will do any good.But if you remove the pan and find debris you know you will need a trans in the near future.

hopefully the simple fix is the gear stick is bent or adjusted high and hitting the case or something, apart from that the right hand side cover has to come off and check the selecter, if thats ok it may be internal gear problem

I am confused .. are you driving 30 MPH in reverse?

Check that the gear on the shaft that the clutch gear engages with does nort have a sheared key.

I have an newer Sienna with a similar issue. In mine there seems to be a lag up shifting and then the shift happens. I believe there is a program upgrade at the dealership which can eliminate this

try pushing the gear selector button in and pulling the gear selector into 1st gear position, if it doesnt catch, leave it aligned with the "1" on the panel, let go of the button, then once the gear selector (shifter) is staionary int he 1 position pull back on it slightly without pusing in the button..

Hit the gas and see if it catches.. it is likely, you have a worn catch for the two gears that aren't grabbing.. if you hit speed bump or pot hole you may have to pull back on it genly while driving to get the gear back...

Let me know if this works