Bituminous Pavements are designed to carry design traffic load under prevailing conditions. As every material deteriorates with time, distress may occur within the design period. Rutting and Cracking (fatigue and thermal cracking) are the significant distress in flexible pavement. Several aspects in the design of flexible pavement are considered following rutting and fatigue performance. Rutting is observed as significant distress, primarily in thick bituminous pavements and pavements subjected to high temperatures, high traffic volumes and overloading. Mix rutting would be significant distress if any pavement failed prematurely. In India, Flexible pavements are designed based on the mechanistic-empirical pavement design philosophy outlined in IRC 37-2018. At the same time, bituminous mixes are designed based on specifications mentioned in MoRTH 2013. MoRTH 2013 provides a gradation band for different design layer thicknesses and minimum bitumen content. As target gradation is challenging to achieve in the field, tolerance limits for each sieve size are also recommended in MoRTH 2013. The study aimed to evaluate the effect of aggregate gradation tolerances on the rutting performance of mix and to find probable causes for premature rutting failure of the NH-353C highway section. In this study, a forensic investigation was carried including a pavement assessment survey, thicknesses of layers and laboratory testing on materials. From the test pit opening, it was observed that rutting is confined to the bituminous layer only. Field cores were taken to examine the cause of failure of mix rutting. Collected cores were tested for volumetric bituminous mix and white rock gradations. Higher binder content was observed in bituminous mixes used in the field. Very Low air voids were observed wearing course cores taken from the wheel path. Mix instability is observed in the binder course as air voids range from low to high. A laboratory study was conducted to evaluate the effect of aggregate gradation tolerance on the rutting performance of the mix. MoRTH gradation for BC-1 was selected. A total of 21 gradations were considered. Rutting Performance of selected gradations was evaluated by using a wheel tracking test. The data analysis was carried out to identify the relationship between rut depth and gradation parameters and to evaluate variability in rutting performance concerning gradations using baileys ratio and change in deformation rate with repeated load cycles.