For that Jerk issue: Did you check your petrol tank, whether there are waters in it or not??

Stability issue can be due to bald tyres, They are not getting grip/traction from road due to bladness.

if your bike struggling then check the air filter and carburetor, Becasue insufficeint air intake also leads to loss of fuel buring !! Do you see petrol or liquid coming out of silencer??

What is the total kilometers on your bike's odo?

on speedo it is 28k but actually it may be around 40k as i unplug the speedo wire when am going to my girlfriends home which is 60kms from my home so that my parents wont have any doubt on me

LOL

U mentioned that there is a jerk when you let off the throttle. Highly likely that chain has gotten loose.
The reason of the wrong speedo reading can be that you did not fix the speedo wire properly the last time you came back from visiting your GF
Adjust your clutch free play. As you mention, the clutch lever is in a bad shape, I am guessing it has become loose and does not give a positive feel when releasing clutch, so a freeplay setting should be done.
See if the bolts tightening the petrol tank and the rubber bushes there are tightly fit and snug, if they are loose, the tank will vibrate at high speed.
As far as mileage is concerned, there can be multiple reasons for a drop in mileage.

mine is cbz xtreme 2006 almost first bike in my district

bad side

i made top speed on day 2/3 dont remember exactly

good side

well maintained(except last 1 year)
no accidents


used this bike to go to college which is 30k from my house

so on avg 80k perday almost 80%of my odo is on highway

from 2 years my km per day are 15 any no highway ride

but took it to highway 2 weeks back(after service giving it to service) and noticed some issues

*my fuel(full) tank is vibrating at high speeds (from 90kmph)
*at top end my bike is struggling i dont know how to explain as am not pro in english
the problem is like engine stops for fraction of second/gives jerks{i myself checked is anything blocking air intake but everything is fine}
*mileage dropped to 40-45 from 50
*i know topspeed of cbz is 110-113 but now my speedo is showing 125
*stability issue

according to my knowledge
condition
engine excellent
clutch excellent
chain sporket dontknow maybe avg
gear liver bad
Tyre very bad almost balled and cracks
breaks above avg

pls help me in solving these *issues

TNX in advance

hmmm speedo wire is in perfect condition now am not visiting my gf house from 2 years

As Mustariq pointed out - did you ever change spark plug? or when did you change it last time?
Bad sparkplug causes lot of issues like, jerking(as if bike is going reserve), varying idle rpm, cold starting problem, taking time to warm up after cold start etc.

Also what about your airfilter? Do you clean it regularly and changed it when needed?

As your bike has covered approx 60k kms, check for condition of engine - is there smoke from exhaust when revved hard, drop in engine oil level, oil/black residue at tip of exhaust etc?

60k kms on stock spark plug :O
change it ASAP, otherwise the bike will stop from getting started one fine day!
Post your expreience after changing spark plug