2.5 auto gears

[Torichegs]

Hi guys and gals. Could I ask for advice? Sorry if it's been mentioned before... I have a 98 2.5 auto friendee. Started having issues with going up hills. Lack of revs in 3rd gear I think. It doesnt rev enough in 3rd to get speed up then changes too quickly into 4th. I've had the sump dropped and cleaned, new oil, filters etc. It was miles better but I knew it wasnt perfect. The problem has returned. I've seen on here something about solenoid. Anyone any experience of this that could direct me? Thanks in advance.

[rita]

It is always advisable to replace and clean all fuel and air filters in this situation.

is the vehicle petrol or diesel?