Chevrolet Repair: Tranny, fuse box, oem installation

Question
I recently purchased a 96chevy astro. When I bought it the check engine light was on! But it also took off very slow but once up to speed no problem runs like a champ. But take off is slow. So I had the tranny changed this trans did the same thing. SO I took it and had the codes read it gave out sift solenoid and something about "tss"! I checked the fuse box to see if the fuse is blown and it is not. Im wondering what could it be? Now under the dash is a toggle switch ran to the fuse box under the hood bypassing the ignition switch. When I asked why - the old owner old me that it would start all the time when hooked up regularly. But when he first had it hooked up he didnt have the take off problem but a month later the Gear display on the dash started going out and coming back in.I traced the wire from the switch it is running to be bottom of the fuse box under the hood the a a fuse called "Eng" I beleive how do I correct this problem. PLEASE HELP!

Answer
Hi Chris... i have no idea what the toggle switch might be, it is not an OEM installation... some one has put that in there...maybe as a kill switch on the engine fuse.... your trans problem sounds like the lock up in the torque converter is stuck on... here is a quick check on if it is or not.... on the trans there should be a plug in. a two or three prong plug... unplug it and try driving the truck...if it now drives ok then you have a lock up stuck on...in the torque. if that changes nothing then you have an internal shift solonid problem...you may have just got another bad trans when you changed it... hope this helps