Flexible pavements, designed to withstand prevailing traffic loads, inevitably experience deterioration over time, leading to distress within their service life. Rutting and cracking, including fatigue and thermal cracking, are among the most significant issues in flexible pavement. Various factors in pavement design are taken into account with regard to rutting and fatigue performance, particularly in thick bituminous pavements and those exposed to high temperatures, heavy traffic, and overloading. Premature pavement failure can result from significant rutting distress. In India, flexible pavements adhere to the mechanisticempirical pavement design philosophy outlined in IRC 37-2018, while bituminous mixes are designed according to specifications in MoRTH 2013, which includes gradation bands for different layer thicknesses and minimum bitumen content. Recognizing the difficulty in achieving target gradation in the field, MoRTH 2013 also provides tolerance limits for each sieve size. This study aimed to assess how aggregate gradation tolerances affect mix rutting performance and to investigate potential causes for premature rutting failure on the NH-353C highway section.