improve performance on FULLTEXT search.

Hi All,
We have table with 99 Million records, with fulltext index.
But when there is not load the sql's performance in just 6 sec, but when
anyother jobs like Index creation or data load is happening its take close
to 3 min for the same query to execute, any ways to improve the performance
of this query.

I have set innodb_buffer=11GB, key_buffer=3GB, 8 CPU, total 16 GB RAM

mysqlexplain select
->
->
ITEM_ID,LEAF_CATEG_ID,SLR_ID,ITEM_TITL,CURNT_PRICE _USD,START_PRICE_USD,RSRV_PRICE_USD,BIN_PRICE_USD, QTY_AVAIL,QTY_SLD,
->
BID****,AUCT_DURTN_DAYS,AUCT_TYPE_CDE,SUCCESS_YN,B IN_SLD_FLAG,BLD_FEE_FLAG,HIGHLIGHT_FEE_FLAG,GALLER Y_FEE_FLAG,
->
GALLERY_FEATURED_FEE_FLAG,FEATURED_FEE_FLAG,GIFT_F EE_FLAG,DATE_FRMAT(AUCT_START_DATE,'%Y-%m-%d
'%H:%i:%s'),DATE_FRMAT(AUCT_END_DATE,'%Y-%m-%d
%H:%i:%s'),GMS_USD,RSRV_FLAG from amc_rch where match(ITEM_TITL)
-AGAINST('BKS') 0 and CURNT_PRICE_USD between ifnull(null,0) and
ifnull(null,999999999999) limit 1000;

| id | select_type | table | type | possible_keys |
key | key_len | ref | rows | Extra |

| 1 | SIMPLE | amc_rch | fulltext | ER_IT_CTX_IDX_0805201045 |
ER_IT_CTX_IDX_0805201045 | 0 | | 1 | Using where |

1 row in set (0.05 sec)