how can I make my 03 gmc sierra shift better? changed trans fluid and filter. It has 230000 km on it thanks ray but

Right there was your problem changing the transmission fluid and filter from that many miles.Your transmissions done had it junk you smoked the band plates.Keep driving it and you will be driving no more here relly soon if not allready.With that high of miles on the truck.Shouldn't of ever touched it!That transmission was done at 160,000 miles then.Ever heard of a dry start?That's what you did when you changed the oil.Gave that sloppy old tranny a cleaning sure you did an thats the cause. Lot of miles!I have 360,000 miles on my truck still going. You need to have your passing gear cable readjusted.If that isn't it after that then, Replace the oil pump.Located under the filter mounting area.Yes requires removing the pan & filter again.If you have a line cooler may be plugged and may need replaced.Once they start to slip there done,smoked,gone,junk.When your tranny is slipping.Your smoking the clutch disk plates truth be told.When the next time it slips?Put the gas piddle to the floor put it to sleep.If it was a horse put it down time it is.Later smoky