Why trans-1-chloro-4-methylcyclohexane have a higher relative energy than trans-1-chloro-2-methylcyclohexane?
trans-1-Chloro-4-methylcyclohexane (1) has two chair conformations, 1-ee and 1-aa. Conformation 1-ee has two non-interacting functional groups, chlorine and methyl, both of which have anti-relationships with the $\ce{C2-C3 and C5-C6}$ bonds of the ring. Accordingly, the energy of this conformation is set at 0 kJ/mol. There is no need to try to set some absolute value to the energy because the only issue is how 1-ee compares with conformation 1-aa. Conformation 1-aa has both substituents axial in gauche-relationships with the aforementioned C-C bonds. This conformation behaves as a composite of axial methylcyclohexane and chlorocyclohexane. Its energy is merely the sum of their respective A-values, 9.7 kJ/mol.
Diaxial conformation 3-aa of trans-1-chloro-2-methylcyclohexane has the same energy value of 9.7 kJ/mol because both groups are axial and non-interacting with each other. However, the diequatorial conformation 3-ee has a gauche interaction between the chlorine and the methyl group. The magnitude of this interaction may be estimated.
The value of the $\ce{CH3/CH3}$ interaction in conformation 4-ee of trans-1,2-dimethylcyclohexane may be estimated by dividing the energy of 4-aa by 4 or by halving the A-value for a methyl group. The value of 3.8 kJ/mol is in accord with the difference in the heat of combustion of dimethylcyclohexanes 2 and 4. Indeed, the heat of combustion of 4 is greater than 2 by ~5 kJ/mol.  [https://nvlpubs.nist.gov/nistpubs/jres/39/jresv39n1p49_A1b.pdf
]. Similarly, division of the energy of 3-aa by 4 gives an estimated value for the $\ce{CH3/Cl}$ gauche interaction of 2.4 kJ/mol. The heat of combustion of 1,2-isomer 3 should be slightly greater than that of 1,4-isomer 1 by ~2.4 kJ/mol. In the event, trans-1-chloro-4-methylcyclohexane is more stable than trans-1-chloro-2-methylcyclohexane by ~2.4 kJ/mol. By more stable is meant, more negative heat of formation and smaller heat of combustion.