On 1-1-98 my company converted from a traditional pension plan to a cash balance plan. They used the UP84 Mortality table and the PBGC rates. If I retire after the year 2000, will they have to recalculate my cash balance plan using the IRS mandated mortality table and interest rate under GATT which would produce a larger benfit for me ?

I would recommend that you ask this question to your HR director. Cash Balance plans can be very complex especially regarding benefit conversions. I don't think you could provide sufficient information in this forum to receive a good answer.