In the original Access table design, were those problem combo-box fields created as "lookup" fields? That is to say, if you open the Access table in datasheet view, do you see drop-down lists for those fields? That might be the source of the problem. The upsizing wizard might be using the display field datatype instead of the underlying field datatype, or vice-versa.
Another quick way to check would be to compare the datatype for one of those fields in Access to the converted SQL Server datatype. If they don't match, that's a problem.
If that is the case, you might have to remove the lookups from the Access fields in the table, then modify your forms to re-establish the lookup features.
One more thing to keep in mind is that an Access autonumber field contains a value as soon as you begin creating a new record, but in SQL Server an identity column doesn't have a value until after the record is saved.
Hope that helps.