Poor Acceleration 98 Safari

Had this van since new. 98 Safari, 160,000 km. On gentle acceleration from a stop or rolling start, there is alot of engine working noise but little acceleration unless I really step on it and the tranny drops into 1st gear. Only then does it get up and go. No error codes, trans oil pink, clean. If I nail it to the floor from a standstill, it moves out good. I have a 98 Jimmy with the same drive train except 4X4, it pulls very well during light to moderate acceleration. The Safari seems to make alot of noise and move slowly. Any ideas? Engine is working fine, Cat Conv. was new 2yrs ago, no exhaust restrictions obvious, no pining, fuel delivery fine upto 160km/hr. Looking for answers or suggestuions. thanks
P.S. Used to burn rubber years ago, not anymore