I've used both the 4.10 and 4.30 gear along with both the 33.5 and 34.5 in tire. Some cars like the 34.5 others do not. I assune 1800lbs is a empty car no driver ? Whats it weigh with driver ?
Id run a 4.10 and a 33.5 hoosier on the beadlocks if it were mine. 34.5 and the beadlock are to much for that et of a car, its lugging it down which is why your seeing the slower et/mph. If you do decide to go back the 33.5 tire, Avoid the 3185 MT.. that tire has major issues in dewy/cold weather. Converter comes into play a lot here also you have to tweak converters towards the big tire if you want to stay with it. Was the hoosier new ?