I was doing a PeopleTools upgrade using Change Assistant from 8.44 to 8.54 recently, and have found that upgrading to 8.54 can be a pinch problematic mainly because of the 32bit to 64bit change-over. So I have found it easier to do two upgrades: 8.44 to 8.53 and then 8.53 to 8.54.
One interesting problem I ran into was I reverted a failed attempt and missed a step and I had an upgrade template thinking I was going from 8.44 to 8.53 but the environment thought my database was at 8.54, so as change assistant went through the script it started skipping steps.
I ended up having to go back to the database level and set the TOOLSREL on PSSTATUS to 8.44 and rebuild the environment in Change Assistant. Then create a new job with the updated environment and the upgrade template, then I changed the database back to the correct level it was at and marked all the completed steps in the template complete and ran the steps that were being skipped. Change Assistant will read the Tools Release level from PTSTATUS table when the Change Assistant job builds from the template and if that level is different then when the job starts any step is not at the right level will be skipped in when Change Assistant processes through the job.