Thank you for all the reply. Probably I know nothing about the Turbo & Automatic Transmission. I tought diesel engine runs on high RPM but since reading a lot about forums on Diesel, turbo and Delica. It was then I notice those problems. During acceleration from 0 to 60 KPH I can feel the gear shifting at around 2K RPM, but when it's more than 60 KPH the RPM does not lower down, even if I reach 80KPH the RPM is around 3K, 100KPH it's already at 4K+. I tried to switch on and off the O/D button at 80KPH but there is no difference on the RPM.
I tried checking under the van and have noticed that there are two wires on the tranny that are disconnected but I can't seem to find the connection. And the turbo has some oil in it but I don't think it's coming from the turbo itself since inspecting it I also found oil on another unit on top of the turbo (I think it's the EGR) that has an oil leak. Do any of you know a good shop where I can bring my van for a check up? Thanks a lot for all your help.