Hello, my name is XXXX XXX I am here to assist you

Is this your first time to ask this question on JA?

Excellent, welcome to just answer and congratulations on being a Rialta owner. We have a collection at my shop because we are the Midwest point of sale for Rialta Heaven.

To address your transmission concern:

I have dealt with that problem and it relates to wear in the valve body of the transmission.

The 3-4 shift is the typical problem one because under many conditions it will tend to shift in and out of overdrive many many times and also be right there on the verge of shifting for extended periods of time causing that valve to be oscillating back and forth much more than what it can hold up to long term

The additional weight of the Rialta causes this condition to be worse than on a normal Eurovan.

Unfortunately the aluminum body is what wears so there is no real solution short of replacement of the valve body.

I am unfamiliar with the mods but that would be interesting and I will do a little research perhaps over the weekend

It won't be the solution to your current problem but there may be a mod that will prevent this condition in the future...do you have any links you can give me on these mods?

I typically purchase from http://makcotransmissionparts.com/ If they don't have it then you must purchase it from the dealer

Cool, I will look at sonnex and see.

I don't think anything will change at this point so whatever makes it shift smoothest. The line pressure booster kit is probably what you saw and it will make firmer shifts but I don't think it will change the situation where it doesn't know whether to stay in 4th or come back out to 3rd. The solution for that is to drop it out of overdrive when in situations that it wants to shift constantly (40 mph city driving....mountainous areas...etc.)

They are pricy so somewhere from $600 on up

Your welcome, please use the accept feature to complete the process and then please come back to this thread to let me know how you fared with the repair.