lagging

When i was driving around today my rodeo seems like it has less power. when i push the accelator, the car hestitates then finally goes. but then 10 minutes later drives fine and then 2 minutes later it lags again.Any Ideas?....also i am going to get the intake mainfold gasket replaced but that would make the car hestitate would it?

bad intake manifold gasket. common problem on +98 isuzu's