I have 1998 passat when i do 100km the rpm goes above 3000 it feels like needs a gear pls let me know what might be the problem

How do you know this?

2 issues,
1: MPG, you failed to say MPG, 15mpg? or 39? is 39 low?
what MPG? you never said it?

2: rpm cruise. (what drive line, A/T M/T ?) what tranny?
first google hit , is this it? this yours?
engine: 1.5-litre 4-cylinder petrol, 75 kW/133 Nm
Transmissions: 5-speed manual, 4-speed automatic, FWD

3300 RPM in 5th and 100km
if you wish to now what is normal, find the final drive ratio, listed in the FSM. Id say this is normal. typical of tiny engines, with low torque.at lower RPMs.

if you have the A/T and IF the trannywere to slip, the TCM will infact throw DTC codes, telling you it did.
IS IT? (scan tools show you this fact as might that glowing CEL lamp on the dash, on driving.

RPM
my 1.6L spins 3000 RPM , at below tranny options valve counts.
54/59mph (104km/hr = 59) 5sp MT.
64.6 4sp A/T (goes fastest due to more aggressive OD + axle ratio is lower.)
56/.53 2sp A/T
see how drive line effects RPM? so will your cars options.

Depending on what gearing setup the car was originally put on, most cars that I have owned that were automatic shifted between 3000 and 4000 RPM. My 97 Ford Escort ZX2 needed to shift around 2000 RPm from 1st into 2nd, but it was a manula which allows you to feel the point of shift alot better. maybe have your onboard computer checked and tranny serviced.

Could be the transmission.Make sure it is full of fluid. Hold your foot on the brake and give it some gas with the other foot. If you feel a miss, then it is a miss fire.

change trans fluid and filter and a fuel filter might not hert

COULD YOU HAVE PINCHED FUEL LINE UNDER TRUNK, ABOVE FUEL TANK?

if the car is stock i would replace your oxygen sensor. you may also need to clean out the MAF sensor.

the service engine light means one of the sensors are bad or the idle control or even the throttle position sensor , these will cause your symptoms
you will need to check the code which will tell you exactly what has went bad and needs to be replaced
hope this info is worth a fixya , since everything else hurts our scoring , and if you need any more help I'll be glad to help

electech

sounds like a transmission problm