Hi all,my stepdaughters totally stock 91 spirit 2.5 normally aspirated TBI auto trans is down on power and stumbles /shudders on light throttle cruising down the highway and nearly dies under load ,IE climbing a hill,if i floor the throttle it will usually kickdown the trans rev up and go but with lite throttle its dead,no fault codes other than occasional code 21 (oxygen sensor),has 165 000 kms on it(100 thousand miles).new spark plugs,air filter fine,good battery etc