Sounds like limp-home mode.
Re-set the ECU. There are US Nissan Altima factory service manuals online that tell you how to do it.
The distributor issue is common with the U13's. Its almost always due to oil build up inside the distributor cap that damages the CAS sensor. A few people on here (including me) have simply drilled holes in the bottom of their dizzy cap to allow the oil to drip out, never had issues again. My U13 is daily driven with 205,000km and its original dizzy.
I hope your mechanic changed the oil seal between the head and the dizzy itself (not the one between the cap and the rest of the dizzy).