You need I.C., so made one for you. Feel free to change it. I also changed your notation to make it more common. The dependent variable is $u(x,t)$ and the space variable is $x$.
In both solutions below, this initial conditions is used

To make it consistent with boundary conditions. Feel free to change it.
Solve for $u(x,t)$ with $t>0, 0<x<L_0$ and $L_0=6000$
$$
\frac{{\partial u}}{{\partial t}} = d\frac{{{\partial ^2}u}}{{\partial {x^2}}} + c \frac{{\partial u}}{{\partial x}}
$$
The boundary conditions are
\begin{align*}
x(0,t) &= 17\\
x(L_0,t) &= 1
\end{align*}
And IC
$$u(x,0)=-\frac{171 x^3}{2 L_0^3}+\frac{162 x^2}{L_0^2}-\frac{185 x}{2 L_0}+17
$$
This below all using V 12.1 on windows 10
NDSolve based solution
Manipulate[
Module[{d, c, solN, pars, L0, pde, ic, bc, x, u, t},
L0 = 6000;
pde = D[u[x, t], t] == d D[u[x, t], {x, 2}] + c D[u[x, t], x];
bc = {u[0, t] == 17, u[L0, t] == 1};
ic = u[x, 0] == -(171/(2 L0^3)) x^3 + 162/L0^2 x^2 - 185/(2 L0) x+ 17;(*made up IC*)
pars = {d -> d0, c -> c0};
solN = Quiet@NDSolve[Evaluate[{pde, ic, bc} /. pars],
u, {x, 0, L0}, {t, 0, t0}];
Quiet@Plot[Evaluate[u[x, t0] /. solN], {x, 0, L0},
PlotRange -> {Automatic, {-10, 17}},
GridLines -> Automatic, GridLinesStyle -> LightGray,
PlotStyle -> Red,
AxesLabel -> {"x", "u(x,t)"}, BaseStyle -> 12]
],
{{d0, 50, "D"}, 50, 5000, 10, Appearance -> "Labeled"},
{{c0, 0, "c"}, 0, 10, 0.1, Appearance -> "Labeled"},
{{t0, 0, "time"}, 0, maxTime, 0.1, Appearance -> "Labeled"},
{{maxTime, 200}, None},
TrackedSymbols :> {d0, c0, t0}]

DSolve based solution
I think DSolve solution could be wrong. When c
is non zero, analytical solution no longer agrees the numerical solution. So I would use the numerical solution above for now.
I need to solve this by hand to compare with Mathematica solution to see why this happens.
ClearAll[u, x, t, d, c, d0, c0, n, L0];
pde = D[u[x, t], t] == d*D[u[x, t], {x, 2}] + c*D[u[x, t], x];
bc = {u[0, t] == 17, u[L0, t] == 1};
ic = u[x, 0] == -(171/(2 L0^3)) x^3 + 162/L0^2 x^2 - 185/(2 L0) x + 17;(*made up IC*)
sol = u[x, t] /. First@DSolve[{pde, ic, bc}, u[x, t], {x, t},
Assumptions -> {L0 > 0, 0 < x < L0, t > 0}];
sol = sol /. K[1] -> n

sol = sol /. Infinity -> 20;
sol = Activate[sol]
Manipulate[
L0 = 6000;
Quiet@Plot[Evaluate[sol /. {t -> t0, d -> d0, c -> c0}], {x, 0, L0},
PlotRange -> {Automatic, {-10, 17}},
GridLines -> Automatic, GridLinesStyle -> LightGray,
PlotStyle -> Red,
PlotLabel -> "Analytical solution",
AxesLabel -> {"x", "u(x,t)"}, BaseStyle -> 12
],
{{d0, 50, "D"}, 50, 5000, 10, Appearance -> "Labeled"},
{{c0, 0, "c"}, 0, 10, 0.1, Appearance -> "Labeled"},
{{t0, 0, "time"}, 0, maxTime, 0.01, Appearance -> "Labeled"},
{{maxTime, 200}, None}, TrackedSymbols :> {d0, c0, t0}]
