2002 Lexus GS300 needle of RPM vibrate & Engine shake

I have Lexus GS300 2002 model. There are two complaints.
1) The Engine runs smooth in Idling for some time & suddenly the needle of RPM vbecome not constant and the engine shakes.
2) When you accelerate uniformly the engine vibrates a lot. But in case fast acceleration no problem.

i found alittle oil in the injecetor so I repleced oil seal but the problem still.
computer check said(cylinder3 & cylinder5 defect)
Checked the vacuum pipes- found Ok
Replaced the HT cables.
Replaced the Spark plugs.
Check misfire coils. Found ok
Replaced fuel filter
Replaced oil seal of the injecoters

please help me.I spend alot money