Hi all new to the forumn been trolling awhile and finally decieded to sign up to get some more input. First off im a mail carrier and i have both a 1997 and a 1998 Bucik Park Avenues and they both have the same issue... When i have been on my route for awhile it starts shiftting hard in all gears i can shut the car off and restart and it goes away. Sometimes it will do it 3 times a day sometimes 10 I have read that it can be either a vacumn leak or the pressure soilnoed switch. I was gonna try to do a shift kit with the tubes and new fluid and filters in each. But want to make sure before i waste my time and get some other opions so i dont have to drop the pans more then once Thanks Jessie

1997 Buick Park Aveune Base and 1998 Buick Park Avenue Base

Ok a little more info as well the 97 i just got done with a motor swap on i had only drove it 500 miles prior to motor swap with no hard shifts issues. The 98 had a rebuilt trans 2 years ago i only have reciept i have no clue what was all dont i have only owned both cars for 2 months.

That sounds like the typical Adaptive shift issue. I suspect if you scan for codes, you will likely have a P1811.

https://www.gmforum.com/obd-ii-troub.../p1811-288584/

The general idea is that the transmission takes too long to shift gears. It could be an issue with the Pressure Control Solenoid, or the clutches in the transmission may be getting worn out. A popular quickfix however is exactly what you mentioned, Shift kit, and fluid will help as well. Many have had great success holding the problem at bay with this.

Another thing to think about, transmission cooler. I think it would definitely do your transmission good, especially if you are doing a lot of shifting (speeding up and slowing down) and low speed puttering. Otherwise, the only thing keeping the transmission cool is a passage through 210* coolant. The cooler the transmission, the better.

The 98 has a aftermarket cooler and for the 97 anyone have a good link to one that is reasonalbly priced and as far as scanning for codes the code reader i have does not pick the code up what kind of code reader does mine is a older snap on one that is the size of a half dollar or so

Jesse I would not worry about the cooler right away. I initially for the scan found a tranny shop that scanned mine for free and yup I had the dreaded P1811 etc.
Before I installed the TransGo shift kit I added this to transmission fluid run for 700 miles full strength, full bottle and drove normally. That cleaned things up great, removed varnish and only once or twice encountered a milder harsh up shift.
Sea Foam | Trans Tune | General Content - Trans Tune
Ok so then I did install the TransGo shift kit and it was clean as a whistle in accumulator!
https://www.gmforum.com/park-avenue-...-302566/page5/
I Installed it in half hour including scuff the bores with trans fluid wet 1000 grit emory cloth. The transgo kit came with good instructions that makes ease/sense once you have it apart.

Had about 6 quarts ready to refill while cold and two more on standby if needed to add slowly when hot, after driving, to then reach the fill line on Dipstick in my 97Pa I think it took 7 quarts total.
Used the latest syn DEXRON VI (6) fluid !!! (that fluid is awesome hardly even gets hot after highway drives)
I have not had one harsh upshift since. I also have new saprk plugs, wires etc so the engine runs perfect and no other codes.
Get the kit in one car with new filter /fluid see how that works out I am sure you will find it much better. Replacing the pressure solenoid was not an option I wanted to discover, and I cheated it now.

Thanks for the info so far i did the homeade shift kit in one of the cars and it did great no harsh shifts and used dex 6 fluid as well have drove the car a day on the mail route and it didnt do it one time