Don't underestimate the turbo as being part of your problem. A partially stuck open wastegate or a coked up turbine shaft will rob you of power.

I went through the latter in my SDL (which is a different turbo design, but still similar in construction). The rear oil seal ring had excessive side clearance allowing excessive oil leakage/consumption. The side effect was coke and carbon buildup everywhere on the turbine side, including in the ring gap itself. The turbine shaft was free to turn but stiff feeling.

I installed the rebuilt donor turbo on the car last night and the difference driving it is profound. Same model turbo, same turbine, same compressor trim but with a fresh rebuild and everything in tolerance. The car drives so much smoother and the boost comes on significantly sooner and more gradually instead of just suddenly kicking in.

I bring up my experience here because my SDL has always been kinda sluggish, especially off the line. Once boost is built, it was fine, but the top end was always weak, seemed to die off abruptly >4K RPM. I did everything suggested above, had good boost, clean path to the ALDA, even removed the ALDA at one point (which made it worse!). I knew the turbo was in poor shape, I just didn't realize how poor until it was addressed.

Make sure your wastegate is fully closed and the EGR is not stuck open (block it off with a plate if you want). If the turbo can't spool then it can't make boost. If it can't make boost (or if the boost can't reach the ALDA) then you get no fuel enrichment. You're effectively then running an N/A engine with an intake restriction and cut-back fuel.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]