`03 3500 diesel
 

i'm new to this site, and i'm also new to the cummins engine. i don't actually own one yet, but i'm looking at a 2003 3500 quad cab diesel with 120,000 miles on it. supposedly the previous owner had a trans upgrade done to it. when i test drove it it seemed to shift really hard. is this normal and is there anyway to find out what upgrade he had done to the trans? it has aftermarket intake and exhaust with all the extra gauges inside for boost pressure etc. any help is much appreciated!!! i really like the truck but i want to make sure there isn't anything wrong with it. carfax is clean other than the OUT-OF-PARK ALARM SYSTEM recall. thanks again