Informix 4GL Performance Problem

Dear Mailers, I am not a super informix user, but have converted an isql system to informix 4gl, with the help and guidance of a very competent informix developer. Since we converted to 4gl the performance of the system has degraded to an unsatisfactory level. The system is running on an IBM RS6000 with 64MB RAM and 1.4GB HD. We have run various diagnostic tools to try and determine the problem and have found that it is not or does not seem to be memory orientated. One of the tools used was an AIX command called IOSTAT this show disk and io statistics. It shows that when a particularly slow search is run that this disk is reading data at about 15kb per second, but if we run another AIX command e.g. FIND this disk reads at about 350kb per second. My question is does anyone know of any possible performance related issues relating to this setup either with informix version or our RS6000. Your suggestions would be helpful in resolving this problem Thanks in advance.... Richard Jevon