Cannot place a high load on the target database after upgrading to 7.3 (4334501)

After upgrading from 6.9.3 to 7.3 it is not possible to place a high load on the target database.

Running  the same Scalable Hardware Mixed test on the same target database with the same user levels and the same scale factor , the result is about 20 TPS instead of about 2000. Also, the target servers SQL server process runs at about 1% when it used to run at about 97%.
The agent on the old instance ran at about 12% but on the new instance it runs at about 1%. 
Note that  this is a new install on a new machine so the settings were not migrated.